High Occupancy Vehicle Lanes

This measure was updated by INSTITUTE FOR TRANSPORT STUDIES (ITS) in 2014 under the CH4LLENGE project, financed by the European Commission.


High Occupancy Vehicle (HOV) lanes are designed to discourage single or low occupancy car use by providing priority to vehicles with more than a minimum number of occupants (usually two or three) and to buses. They encourage car sharing or public transport use, or both, by allowing users to reduce their journey times relative to single-occupant vehicles, particularly when the general purpose lanes are congested. This in turn reduces the number of cars on the network and this reduction in the demand for road space can reduce overall congestion, fuel consumption and environmental impacts. They have become much more widespread in the last 10 years in the USA and are slowly but increasingly being implemented in Europe. 

An HOV lane can be created by converting an existing multi-user road lane into an HOV lane (for all or part of the day), by adding an extra inside or outside lane to an existing road or by converting an existing bus way or bus lane into an HOV lane.

HOV lanes can be a part of motorway (as is common in the USA) or of a major arterial road (as in Leeds, UK). They can be ‘tidal’ to help the traffic in the busiest direction (usually inbound towards city centres during the morning peak, outbound during the evening peak). They can be permanent and separated by a physical barrier from the general purpose lanes or may be defined by purely non physical means such as lane markings and special traffic signs. The hours and days of HOV lane operation can vary depending on the congested hours and function of the road stretch to which they are applied; for example during morning peak hours only, on weekdays or at all times.

Conclusions on the effects of HOV lanes vary from one study to other. They have been reported to reduce vehicle trips on HOV corridors by between 4 per cent and 30 per cent. It has also been reported that willingness to share cars and to use buses increases after the opening of an HOV lane. There is evidence that HOV lanes are more effective in these terms in cases where delays to general traffic due to congestion are greatest. There is, however, also a view that HOV lanes may be less effective in some cases than general purpose lanes.

Description

High occupancy vehicle lanes are designed to discourage single/low occupancy car use by providing additional priority to vehicles with more than a minimum number of occupants (usually two or three) and buses. They encourage car sharing and/or public transport use by allowing users to reduce their journey times relative to single-occupant vehicles, particularly when the general purpose lanes are congested. This in turn reduces the number of cars on the network and this reduction in the demand for road space can reduce overall congestion, fuel consumption and environmental impacts. They have become much more widespread in the last 10 years in the USA largely because legislation restricts the construction of mixed use roads in areas that fail US National Ambient Air Quality Standards.  

In Britain, the National Travel Survey shows that between 1997 and 2002, average car occupancy rate dropped from 1.6 to 1.58, and single car occupancy is highest for commuting trips (85%). HOV lanes offer potential for making more efficient use of road space, especially at peak times, by increasing the attractiveness of public transport and retaining the flexibility and comfort of the car.

Two-wheel vehicles (motorcycles and/or bicycles) are usually permitted to use the HOV but this may vary between locations.

An HOV lane can be created in three different ways (ICARO, 1999):

  • an existing general purpose lane can be converted into an HOV lane (temporarily or permanently);
  • an additional inside or outside lane can be added;
  • an existing bus way/lane can be converted into an HOV lane.

Such schemes can therefore be considered as either preventing single-occupancy cars from using all of the available road-space or as providing additional road capacity for buses and HOVs.

HOV lanes can be a part of motorway (as in the USA) or major arterial road (as in Leeds, UK). They can be ‘tidal’ to help the traffic in the busiest direction (usually inbound towards city centres during the morning peak, outbound during evening peak). They can be permanent and separated by a physical barrier from the general purpose lanes or by purely non physical means (lane markings, special traffic signs, etc. (see illustrations below). The hours and days of HOV lane operation can vary depending on the congested hours and function of the road stretch to which they are applied e.g. morning peak hours only, on weekdays or at all times. 

In the USA there are now nearly 2,300 miles of HOV lanes

HOV lanes cover 60-mile of the I65/75 in Atlanta (picture above).

There are close to 100 HOV projects on freeways and in separate rights-of-way in 30 metropolitan areas in North America. A list of the HOV lanes and their details (e.g. length, number of lanes, time of operation) can be found at the Transportation Research Board: HOV Committee website (available at http://www.hovworld.com).

A Typical HOV lane in the USA

Changing the direction of a HOV lane

Courtesy of Transportation Research Board (http://www.hovworld.com/photos.html)

Terminology for HOV priority lanes generally also covers bus-only lanes (bus priority lanes). However, here we restrict attention to dedicated HOV lanes which both buses and ‘high’ occupancy private vehicles are allowed to use. 

High Occupancy Toll (HOT) lanes are extensions of HOV lanes where ‘low’ occupancy vehicles (LOV) are allowed to use the lane if they pay a toll (or an increased toll) (Parsons Brinckerhoff, 2003). 

Technology

Technology related to HOV lanes other than their construction is mainly related to their enforcement. It is generally necessary to allow HOVs to use both general-purpose and HOV lanes and to switch relatively freely between them. If the general-purpose lanes are congested and the HOV relatively free-flowing, there will be temptation for low occupancy vehicle (LOV) drivers to violate the HOV lane regulations. The success of the HOV lane operation therefore depends critically on appropriate enforcement. HOV lane enforcement involves determining eligibility to use an HOV facility by observing the number of vehicle occupants and penalising those who violate it. Recently, automated occupant observation technologies have been under investigation.

The ENTERPRISE program (see http://enterprise.prog.org) has been investigating ITS technologies for HOV lane enforcement. Possible options include outside observation technologies such as digital cameras, multi-camera video recorders, infrared radar machine vision and automatic vehicle identification. In the future, there may be some in-vehicle observation technologies available for HOV lane enforcement, but as yet no wholly-satisfactory solution has been found.

In the meantime, manual observation of vehicle occupancy will be required. Where the HOV lane is physically separated from other lanes, random police controls at the entry or exit of the lane are usually relatively straightforward. Enforcement of HOV lanes with no physical barriers is more difficult. Alternatives include random checks by the police or other enforcers observing the use of HOV lanes and/or simply encouraging other drivers to report HOV lane violators. The latter approach obviously runs into difficulties if violators choose to simply deny an alleged violation.

Enforcement is crucial for gaining public support for HOV, but providing manual enforcement is expensive and takes the police away from their core work, while automated systems are still unproven. In Leeds, the cost of continuous police enforcement was a factor in the decision to restrict the lane to peak period operation.

Why introduce HOV lanes?

In theory, HOV priority lanes can be an efficient way of using road capacity as they discourage inefficient use of the road space by single occupant cars by giving priority to public transport, two-wheel vehicles and car sharing. If every single occupancy driver can be persuaded to car-share, then the people-moving capacity of a given road will be doubled, and additional benefits will accrue from any that switch to van-pools or existing public transport services.

This is illustrated in the figure below.

Number of vehicles needed to carry 45 people.

Courtesy of Southwest Washington Regional Transportation Council (http://www.rtc.wa.gov/hov/).

They can also represent a more equitable use of road space, since they allocate more of the available road space to HOVs and buses which impose less congestion per-person-trip on other road users than Single Occupancy Vehicles (SOVs) (VTPI, 2004). 

However some argue that they can be less efficient than additional road capacity for all users (Orski, 2001; Dahlgren, 1998; Johnston, 1996). Wellander and Leotta (2001) report that effectiveness and benefits of HOV lanes depend on the criteria and assumptions used to evaluate them. This would also change according to type of HOV facility (e.g. additional or converted lanes). Some oppose additional lanes on the basis that they increase total road capacity and encourage longer-distance commuting and in some cases people believe that HOV lanes can have negative impacts (Leman et al 1994; Dalhgren, 1998). Moreover, HOV lanes can often take years to reach their full potential, since they affect long-term decisions such as where consumers live or choose to work.

There are various studies related to the evaluation of HOV lanes which are mainly based on US experience of existing HOV lanes, and on modelling studies. Status of HOV lane developments in Europe is discussed in ICARO (1999).

Conclusions and results vary from one study to other. There are numerous reports and papers available at the TRB HOV committee website at http://www.hovworld.com. Arguments on HOV lanes can be divided into three groups. However it should be noted that the arguments also depend on whether the HOV lanes are “converted” or “added” lanes.

Those that find that HOV lanes are effective

Level of reduction in vehicle trips on HOV corridors is reported to vary between 4 to 30% (e.g. Comsis, 1993; Pratt, 2000; Ewing, 1993). Apogee (1994) estimated that HOV lanes can reduce up to 1.4% of vehicle miles travelled (VMT) and up to 0.6% of vehicle trips in a region. For example, in Texas, HOV lanes carry as much as 40 percent of the people moved on the freeway. Surveys have shown that willingness to car share and use the bus  increases after the opening of an HOV lane (Stockton et al, 1999). Similar results are also found in the UK first HOV lane in Leeds (LCC, 2002) (see Evidence on Performance section).

While some theoretical research has suggested that maximum delays of 30 minutes are necessary to justify an HOV lane over a general purpose lane (Dalgren, 2002) other monitoring results show that as little at 10 minutes delay can result in very successful HOV lane operation (Stockton, 1999). For example, currently the Shirley Highway (Virginia)’s 28-mile reversible HOV lanes carry an average of 10,400 person trips and 2,800 vehicles in the morning peak hour. These lanes provide average travel time savings of 31 and 36 minutes for the morning and evening peak travel periods.

Those that find HOV lanes to be less effective than general purpose lanes

Orski (2001) argued that HOV lanes are less effective than additional general purpose lanes. By using a simulation model based on the Sacramento Area Transportation Study, Johnston et al (1996) also argue that benefits of HOV are generally temporary and that the higher speeds soon induce longer non-work trips, time shifting to peak periods, mode shifts from bus to HOV and abstraction of non-car-available travellers from PT to join SOV drivers. The study results also show higher VMT with the new HOV lanes. 

Similarly, based on the model results for an hypothetical corridor study, McDonald et al (2000) concluded that “construction of new mixed flow lanes or conversion of existing HOV lanes can lead to increases in VMT that are likely to have negative environmental impacts. This occurs due to modal shifts and rescheduling effects without consideration of possible inducement of new trips”. This study also argues that “HOT (High Occupancy Toll) lanes offer the possibility of larger reductions in vehicle and person hours of travel time, because they preserve incentives for higher vehicle occupancy and allow more efficient use of lane capacity”.

Dahlgren (1998) argues that reduced delays for both HOV and LOV can induce additional traffic growth, shifts from other routes and times. He summarises the possible effects of constructing a HOV lane as illustrated in the figure below 
Possible effects of constructing an HOV lane (Dahlgren, 1998)

HOV lanes and HOT lanes

Despite the widespread implementation of HOV lanes in other major US cities and inter-urban corridors, ridesharing amongst commuters has been declining – from 20% in the 1970s to 13% in the 90s – and under-utilisation has led to criticism of HOV lanes. This has led to increasing interest in High Occupancy Toll (HOT) lanes and studies have increasingly demonstrated that HOT lanes with toll differentiation provide a cost-effective way to reduce traffic congestion (e.g. Turnbull et al., 1991; O'Sullivan, 1993; Yang et al, 1999). The HOT lanes scheme in San Diego in the USA costs sole drivers up to $4, depending on distance, and HOVs with 2+ occupants can travel free. In Houston, Texas, the HOT scheme allows HOVs with 2+ occupants to use the HOV 3+ lane for a fixed fee.

Demand impacts

The table below illustrates ways providing an extra HOV lane might be expected to affect the number of car kilometres travelled.

Likely Impact of an Extra HOV Lane on Car Km

Responses and situations
Response Reduction in road traffic Expected in situations

Because of reduced delays in peak hours, some trips might be shifted to those hours.

/

The extra lane for HOVs may allow these vehicles to switch to a more-direct HOV route from a more- indirect route chosen previously to avoid the congestion

Conversely, the extra capacity may encourage HOV drivers to choose a longer (but faster) HOV-lane route in preference to a more-direct but more-congested alternative.

/

Increased accessibility of locations (e.g. work, education) might have positive or negative effects in relation to planning policies.

The impact of an HOV on accessibility is unlikely to be large enough to significantly change overall trip frequency.

The bus-lane component of the HOV will help encourage mode-shift from single occupant cars to buses.

/

Reduced car ownership through car sharing.

Induced car ownership due to reduction in delays from the extra road capacity.

HOV lane corridors can become attractive to commuters due to time savings. This is likely to increase car kilometres due to the impact of the additional road space.

= Weakest possible response = Strongest possible positive response
= Weakest possible negative response = Strongest possible negative response
= No response

The table below illustrates ways in which excluding Single Occupancy Vehicles (SOVs) from a lane on a moderately-congested link might be expected to affect the number of car kilometres>travelled.

Likely Impact of Excluding SOVs to create an HOV Lane on Car Km

Responses and situations
Response Reduction in road traffic Expected in situations

Reduction in capacity for SOVs might encourage some of these trips to avoid the congested peak periods

/ Reduction in capacity for SOVs will encourage them to divert to longer alternative routes but this will partially compensated by the improved priority forHOVs - the net effect will depend on the SOV/HOV mix on the current link.
/

Decreased accessibility of locations (e.g. work, education) for SOVs might cause them to switch to more-distant locations but this will be compensated for by the improved priority for HOVs- the net effect will depend on the SOV/HOV mix on the current link.

The impact of removing highway capacity from SOVsmight cause some trip suppression

The bus-lane component of the HOV and the loss of capacity for SOVs will help encourage mode-shift from single occupant cars to buses.

Reduced car ownership through car sharing

Reduction in attractiveness of SOV-commuting may encourage some to move to reduce the duration of their commuting journey

= Weakest possible response = Strongest possible positive response
= Weakest possible negative response = Strongest possible negative response
= No response

Short and long run demand responses

For the average individual, the general impact of providing an extra HOV lane might be as the following:

Demand responses

Response

-

1st year

2-4 years

5 years

10+ years

/ /

Change job or house location

/ /  

Ride share

-

Public transport

-

Walk/cycle

-

/ /

-

/ /
= Weakest possible response = Strongest possible positive response
= Weakest possible negative response = Strongest possible negative response
= No response

Supply impacts

Supply impacts depend on the way in which HOV lanes are constructed. If they are ‘converted’ lanes, then the supply for general purpose traffic decreases. If they are ‘added’ lanes then the supply for both HOV and LOV increases. If they are ‘reversible’ lanes then the supply for the contra-flow traffic decreases.

Financing requirements

Costs of HOV lanes include project construction, management and enforcement. These costs depend on the type of HOV lanes, e.g. converted or added. While converting an existing general purpose lane into a HOV lane is relatively cheap, constructing a new lane can be expensive, especially if physical barriers are included in the HOV lane scheme.

Accompanying measures, such as marketing, consultation etc. can also be costly. Enforcing the measure can also involve substantial costs. Usually, there are no sources of income associated with the HOV lanes. A possible source of income could be the introduction of a combined HOV lane / pay lane (HOT lane), where solo drivers are also accepted upon payment of a toll, which can be varied according to the time of day and the level of congestion.

HOV can be a relatively low-cost measure; the Trondheim scheme, for example, cost 750,000NOK (£60,000) for signing, markings, information and marketing. In comparison, many of the American states have spent close to $1m (£550,000) in information campaigns alone.

Expected impact on key policy objectives

Expected benefits of HOV lanes include increased travel speeds and reliability for HOV passengers (including those using public transport), increases in car occupancy and person throughput. It makes the alternatives to driving alone more attractive. They are also perceived to provide significant benefits to local authorities including road and parking facility cost savings, public transport operating cost savings, congestion and pollution reductions, and consumer benefits (VTPI, 2004).

However some argue that HOV lanes (as extra road capacity) encourage urban sprawl and contribute to poor air quality (Leman, Schiller and Pauly, 1994) and they are an inefficient use of road capacity (Orski, 2001; Johnston, 1996).

The impact of HOV lanes tends to be measured in terms of improvements in car occupancy and person throughput, and there are few direct measurements of congestion. In many cases, quoted journey times and hence delays to carsharers have improved, but in some case this is at the expense of the mixed use lane. 

The attractiveness of the lanes largely depends on journey time differentials, but this is constrained in an urban setting by buses stopping in the HOV lane, junctions and access by frontagers, etc. Another key variable is people’s propensity to rideshare. Research in the US has shown that this is not linked to socio-economic characteristics, but that trip lengths and the ease of finding a partner are important. The latter is likely to become more difficult as more employees work flexibly.

The contribution of the provision of an extra HOV lane to policy objectives are summarised below.

Contribution of an Extra HOV Lane to Policy objectives

Contribution to objectives

Objective

Scale of contribution

Comment

  By benefits exceeding the costs by far when all impacts included e.g. time savings for both HOV and LOV passengers
  Wider streets, faster traffic, more capacity for cars
  / Reduction in congestion & encouragement to car-share, so potentially reducing total vehicle kms, offset by impacts of the extra road capacity on inducing additional car trips
  Greater time savings for those who have to use public transport or car share
  Depending on the design features but there can be conflicts between vehicles in higher-speed HOV lanes and vehicles in lower speed general use lanes. Pedestrians may also find it more difficult to cross the wider streets with its faster traffic
  Difficult to evaluate, unlikely to be significant
  Requires public funding for construction and ongoing enforcement unless it is converted into HOT lane facility.
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

The policy contribution of excluding SOVs from an existing moderately-congested link are summarised below.

Policy Contribution of Creating an HOV by Excluding SOVs

Contribution to objectives

Objective

Scale of contribution

Comment

 

Restricting existing road capacity is likely to create more journey-time losers than winners (unless the benefits of the extra bus priority are significant enough to create significant mode-shift).

 

More congestion, combination of fast (HOV) and slow (SOV), unless the resulting switch to PT and/or car sharing is significant.

  /

Increase in congestion offset by the encouragement to car-share or use the bus.

 

Greater time savings for those who have to use public transport or car share.

 

Depending on the design features but there can be conflicts between vehicles in higher-speed HOV lanes and vehicles in lower speed general use lanes. Pedestrians may also find it more difficult to cross the road because of the mix of fast and slow traffic.

 

Difficult to evaluate, unlikely to be significant.

 

Requires public funding for implementing and enforcing the exclusion of SOVs (unless it is converted into HOT lane facility).

= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Expected Impact on Problems

The impacts of HOV lanes will be largely determined by the relative proportion of SOVs to HOVs in the traffic, the speed-differential between general and HOV lanes, the nature of the traffic using the route (in particular whether origins and destinations are sufficiently limited to make car-sharing a realistic alternative for a significant proportion of the SOV drivers). The pattern differs between providing an extra HOV lane and restricting the use of existing lanes.

The table below relates to the provision of an extra HOV lane.

Contribution to alleviation of key problems

Problem

Scale of contribution

Comment

Congestion

Time saving for those who able to use the HOV lanes.

Community impacts

Wider roads, faster traffic.

Environmental damage

Construction of the extra lane.

Poor accessibility

By reducing public transport journey times and increasing its reliability and favouring low-car-ownership households.

Social or geographic disadvantage

By improving access.

Accidents

Increased speeds and conflicts between HOV and LOV may cause accident risk, pedestrians may also have more difficulties crossings.

Economic growth

By improving access, but impacts small.

= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

 

The table below relates to the restriction of SOVs from an existing lane.

Contribution to alleviation of key problems

Problem

Scale of contribution

Comment

Congestion

Time saving for those who able to use the HOV lanes likely to offset disbenefits to SOVs.

Community impacts

Faster traffic.

Environmental damage

/ Some reduction in traffic, but offset by increased congestion on SOV lanes.

Poor accessibility

By reducing public transport journey times and increasing its reliability and favouring low-car-ownership households.

Social or geographic disadvantage

By improving access.

Accidents

Increased speeds and conflicts between HOV and LOV may cause accident risk, pedestrians may also have more difficulties crossings.

Economic growth

By improving access, but impacts small.
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Expected winners and losers

Some argue that HOV priority is unfair as it favours one group (HOV users) over other road users (Orski, 2001). Others consider HOV priority a fairer allocation of road space by giving travellers who use less space, and therefore contribute less to traffic congestion, priority over those who use more space. Some critics argue that HOV lanes do not meet the needs of people who cannot use public transport (VTPI, 2004).

HOV lanes will benefit car sharers and public transport users, which includes a high proportion of low income and disadvantaged people (Pratt, 2000). 

Winners and losers

Group

Winners / losers

Comment

Large scale freight and commercial traffic

/

When delays are reduced in general purpose lanes

When delays are increased in general purpose lanes

Small businesses

When applied with no stopping or parking restrictions

High income car-users

When they use the scheme

People with a low income

Lower-income people tend to rely on public transport and HOVs

People with poor access to public transport

Limited impact.

All existing public transport users

Due to shorter journey times

People living adjacent to the area targeted

Increased accessibility

People making high value, important journeys

/

Winners if car share or take PT.

Losers if general purpose lanes are congested

The average car user

/

Winners if car share

Losers if general purpose lanes are congested

= Weakest possible benefit = Strongest possible positive benefit
= Weakest possible negative benefit = Strongest possible negative benefit
= Neither wins nor loses

Barriers to implementation 

HOV lanes can be controversial and provoke substantial resistance, so not all politicians will be keen on this instrument especially in the case of  ‘converted’ lanes (ICARO, 1999). HOV facilities in the US have closed after a few months of operation because of public opposition (Fuhs and Obenberger, 2001). An example of this phenomenon recently occurred in New Jersey where the State removed HOV lanes on I-287 and I-80 (McDonald, 2000). Arguments include that “they are unfair and ineffective, in preference to general-purpose lanes” or that “they increase total road capacity, leading to increased total vehicle traffic and urban sprawl” (VTPI, 2004). Therefore public and political support is an essential factor for successful application of HOV facilities. Marketing is essential to create awareness and acceptance in reducing traffic congestion and pollution and to promote car sharing (ICORO,1999).

Scale of barriers

Barrier

Scale

Comment

Legal

No legal barriers.

Finance

/ Depends on whether new lane constructed or existing lane converted.

Governance

Usually no split of responsibilities.

Political acceptability

Limited political debate on such measures.

Public and stakeholder acceptability

Some opposition from frontagers and freight operators.

Technical feasibility

Some problems with integration into road network, and with enforcement.
= Minimal barrier = Most significant barrier

Enforcement

Enforcement is crucial for gaining public support for HOV, but providing manual enforcement is expensive and takes the police away from their core work, while automated systems are still unproven. In Leeds, the cost of continuous police enforcement was a factor in the decision to restrict the lane to peak period operation.

Experience in Europe: Leeds, UK

Context

In 1998, UK’s first High Occupancy Vehicle (HOV) lane was introduced on the A647 Stanningley Road and Stanningley By-Pass which form the principal radial route to the west of Leeds city centre and are part of the route linking Leeds and Bradford (see figures below). The scheme was experimental at first but has become permanent. The road experienced severe congestion and there were few public transport priority measures.

The HOV lane scheme covers a total of 1.5km of 2.0km long dual carriageway in two sections. They operate in the morning (07:00 – 10:00) and evening (16:00 – 19:00) peak periods on Mondays to Fridays. Only buses, coaches, other vehicles carrying 2 or more people, motorcycles and pedal cycles are allowed on these lanes (HGVs over 7.5T are not permitted).

Location of the A647 HOV Scheme in Leeds.

Scheme layout, High Occupancy Lane, Leeds. Courtesy of Leeds CC.

Illustrations of the Leeds HOV lane scheme


Courtesy of JMP Consultants Ltd


source ICARO (1999)


Courtesy of Leeds City Council

This project was part of an EU research project called ICARO (Increasing CAR Occupancy). Its objectives were to increase car occupancy by encouraging car sharing; and to demonstrate the feasibility of providing a lane for shared use by buses, other high occupancy vehicles, motorcycles and cycles. More detailed information can be found in the ICARO project deliveries and final report (available at http://europa.eu.int/comm/transport/extra/final_reports/urban/icaro.pdf).

The following summary information is taken from the DfT’s ‘Bus Priority: The Way Ahead’ initiative (case study on HOV Lanes) (DfT, 2004); Leeds City Council’s HOV Fact Sheet (2002); and ICARO (1999).

Impacts on demand

Prior to implementation of HOV lane, 30% of cars on the A647 (Stanningley Road) had 2 or more occupants. With the inclusion of buses, one-third of all vehicles carried two-thirds of all people (2225 of 3645) in the morning peak period. The journey in free flow conditions could take about 3 minutes, regularly had taken over 10 minutes. Therefore a priority lane such as an HOV lane would benefit a majority of the travellers in terms of journey times. However single occupant drivers (total of 1420) would be expected to suffer some additional delay due to capacity reduction caused by the HOV lane. 

The results below based on the ‘Before’ surveys that took place in May and June 1997 and ‘After’ surveys that took place in May and June 1999. Data collected included

  • traffic counts in the morning and evening peak periods;
  • vehicle occupancy;
  • journey times;
  • queue lengths; and
  • personal injury accidents.

In addition to this, public attitudes and driver behaviour information were analysed from household and roadside interview surveys. Air quality was monitored by an environmental monitoring station on the route. 

The following table summarises the results of before and after analysis done by Leeds City Council (LCC, 2002). It was reported that, after an initial reduction, traffic levels gradually increased to their previous levels with about 5% increase in HOVs. This might indicate that there was an exchange of HOV and non-HOV traffic between the A647 and parallel routes. On the other hand, 26% of HOV interviewees were apparently new car pools and cited the HOV lane as the reason for forming them. Relatively low support amongst HOV drivers (about 66%) might have resulted from the fact that these drivers also made peak period journeys as non-HOV drivers. When doing so, they did not benefit from the journey time savings observed.

Leeds HOV lane impacts (Bus Priority Initiative case study, (LCC, 2002))

Indicators

Results

Morning peak traffic flows

(07:00 - 10:00)

Immediately after opening 20 % traffic reduction (due to driver avoidance).

By late 1999, traffic flows returned to prior levels

Sight increase in scheduled bus services, motorcyclists and cyclists

Evening peak traffic flows

(16:00 to 19:00)

10 % reduction at scheme inception

 by June 1999, traffic flows returned to the 'before' level

By June 2002 traffic flow increased by a further 14 %

Occupancy and mode share:

between 1997 and 1999, HOVs in morning period increased by 5 %

Average car occupancy rose gradually from 1.35 in May 1997 to 1.43 by June 1999 and 1.51 in 2002

Bus patronage increased by 1% in the first year of operation (There are indications of further growth in bus patronage since 1998 but no real data available to analyse)

Journey times:

Morning peak journey time savings for buses and other HOVs were 4 minutes (comparing 1997 to 1999 data)

Reduction of 1 minutes in non-HOV journey times in the same period.

Queue Lengths

By giving priority to HOVs, two queues of equal length have been transformed into a long queue in the non-HOV lane and a short queue in the HOV lane

No evidence of non-HOV queues extending

Accidents:

Reduction of 30 % in casualties in a period of three years after scheme implementation.

Enforcement:

Lane violation levels were low in the months following implementation

In 2002, lane violation levels were still less than 6 % despite a relaxation of enforcement.

Public attitudes:

An increase from 55% to only 66 % in HOV drivers support for HOV lane (results from roadside interviews in 1999).

Air quality:

Little change in air quality

A noticeable noise reduction coinciding with both the morning and evening periods of HOV lane operation

The figure below shows the HOV lane journey time change along different sections of A647 that resulted from HOV Lanes and signal improvements. In 1998, morning peak HOV journey time savings were 3½ minutes for a 5km trip from the Leeds Outer Ring Road to the Inner Ring Road. In 1999, the time saving increased to just over 4 minutes. The figure also indicates that the journey time savings starts after the first 2.5 -3 km and changes sharply from time lost to time gain.

A647 AM peak HOV lane journey times

The figure below shows the journey time change on the general purpose lanes (outside lanes) within same sections of A647. In 1999, overall inbound non-HOV journey times did not increase and were total of 1½ minutes shorter in the morning peak for the same 5 km long journey.

A647 AM peak non-HOV lane journey times

Costs

Scheme implementation cost was £585,000 at 1998 prices. Following the success of the A647 scheme, Leeds City Council has now introduced HOV lanes on the proposed East Leeds Link Road.

Experience in Europe: Bristol, UK

On the congested dual two-lane Avon Ring Road near Bristol, the local (South Gloucestershire) Council had wanted to implement a bus lane but frequencies were too low to justify reallocating road space to buses alone. It therefore opened an HOV lane for buses, taxis and cars with 2+ occupants. The lane has been extended from the original 750m to 1.2km in length (comprising two sections separated by a roundabout) and operates in one direction in the morning peak only.

The lane has led to an increase in efficiency; the proportion of single occupancy vehicles has fallen from 80% to 68%, and traffic levels have increased by 10% (as a result of vehicles re-routeing from parallel roads) as the lane has ‘smoothed’ flows and allowed higher throughput.

Journey times for all vehicles have fallen from 20 minutes to 6 in the HOV lane and 12 in the mixed use lane.

Experience in Europe: Madrid

Context

One of the first and more significant European HOV lanes is the 16 km two-lane scheme on the median of the N-VI motorway into Madrid which was opened in January 1995. It was introduced when the motorway was widened to accommodate traffic from nearly affluent suburbs. The lanes are reversed to match peak flows and this has greatly increased throughput of traffic.

Impacts 

A study of operational performance undertaken by the Madrid Polytechnic University demonstrated that:

  • In terms of efficiency, the N-VI HOV lanes were found to be positive as they carry 59.3% of the morning peak hour travellers using 2 lanes, while the 3 lanes of the main roadway carry only 40.7% of the travellers.
  • The proportion of 2+ vehicles increased from 30% in 1991 to 40% in 1996.
  • The lanes have attracted a growth in public transport mode share, rather than ridesharing.
  • The HOV lanes retain high levels of service through most of the peak period because they still have some spare capacity. To fully utilise all available road space, active policies to promote carpooling and public transport use are needed.
  • Public transport use increased by 40% in the period 0700-1000 in the year following implementation and more bus operators have begun operating, so frequencies are higher. Monitoring reports also note a fall in congestion, but there are no actual measures given.

Other results included:

  • For inbound journeys, the average occupancy in cars has increased from 1.36 passengers per car in 1991 to 1.67 passengers in 1997.
  • The modal split in the corridor has changed so that the use of buses has increased from about 17 % in 1991 to about 26 % in 1997. In the same period the use of cars has decreased from about 56 % to about 48 %.
  • Reduced travel times in and out of Madrid has lead to the change in modal shift.

Experience in Europe: Trondheim 

The Trondheim scheme, which opened in May 2001, uses one lane in each direction on a dual two-lane radial on the approach to the city centre. The route was characterised by congestion during the morning and evening peaks which affected the reliability of public transport operations, but the delays were light – typically 5 minutes per vehicle lasting for a period of about half an hour.

Different Trondheim schemes were tested with the American CORSIM model and a 2+ scheme selected to balance usage and speed in the HOV lane and congestion to general traffic.

Nordic Road and Transport Research (No 3, 2001) reports that the HOV lanes offer journey time advantages of only 2-3 minutes in the peaks and yet the proportion of 2+ vehicles has increased from 30 to 40% and there has been a corresponding decline in single occupancy vehicles from 70 to 66%. This survey was limited to the HOV corridor and it was not clear if carpoolers have been attracted from alternative routes.

Traffic levels in the area have remained stable, possibly because some traffic has been attracted from surrounding residential streets, while the number of people using the route has increased and person hours in the morning peak have fallen by 20%.

In the mixed use traffic lane, the congested period has increased from half to three-quarters of an hour; however, the city authority considers this to be acceptable, especially has the scheme helped to regulate stop-start conditions downstream.

Shirley Highway and Santa Monica Freeway, USA

The first major US schemes were the Shirley Highway near Washington DC, which opened in 1973 with two HOV lanes for cars with four or more occupants, and the conversion of one lane of the Santa Monica freeway in Los Angeles to HOV 3+ operation (including buses) during the peak hours.

The successful Shirley scheme now carries half of the commuters in the corridor at an average speed of twice the mixed flow lane. However, the Los Angeles scheme reverted to mixed use after just four months because of poor planning and local opposition.

The case studies largely reinforce the first principles assessments, which are replicated here. Two tables are presented under each heading; one for newly constructed lanes and one for conversions.

Contribution to objectives

Newly constructed lanes

Contribution to objectives

Objective

Scale of contribution

Comment

  By benefits exceeding the costs by far when all impacts included e.g. time savings for both HOV and LOV passengers
  Wider streets, faster traffic, more capacity for cars
  / Reduction in congestion & encouragement to car-share, so potentially reducing total vehicle kms, offset by impacts of the extra road capacity on inducing additional car trips
  Greater time savings for those who have to use public transport or car share
  Depending on the design features but there can be conflicts between vehicles in higher-speed HOV lanes and vehicles in lower speed general use lanes. Pedestrians may also find it more difficult to cross the wider streets with its faster traffic
  Difficult to evaluate, unlikely to be significant
  Requires public funding for construction and ongoing enforcement unless it is converted into HOT lane facility.
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Converted lanes

Contribution to objectives

Objective

Scale of contribution

Comment

 

Restricting existing road capacity is likely to create more journey-time losers than winners (unless the benefits of the extra bus priority are significant enough to create significant mode-shift).

 

More congestion, combination of fast (HOV) and slow (SOV), unless the resulting switch to PT and/or car sharing is significant.

  /

Increase in congestion offset by the encouragement to car-share or use the bus.

 

Greater time savings for those who have to use public transport or car share.

 

Depending on the design features but there can be conflicts between vehicles in higher-speed HOV lanes and vehicles in lower speed general use lanes. Pedestrians may also find it more difficult to cross the road because of the mix of fast and slow traffic.

 

Difficult to evaluate, unlikely to be significant.

 

Requires public funding for implementing and enforcing the exclusion of SOVs (unless it is converted into HOT lane facility).

= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Contribution to problems

Newly constructed lanes

Contribution to alleviation of key problems

Problem

Scale of contribution

Comment

Congestion

Time saving for those who able to use the HOV lanes.

Community impacts

Wider roads, faster traffic.

Environmental damage

Construction of the extra lane.

Poor accessibility

By reducing public transport journey times and increasing its reliability and favouring low-car-ownership households.

Social or geographic disadvantage

By improving access.

Accidents

Increased speeds and conflicts between HOV and LOV may cause accident risk, pedestrians may also have more difficulties crossings.

Economic growth

By improving access, but impacts small.

= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Converted lanes

Contribution to alleviation of key problems

Problem

Scale of contribution

Comment

Congestion

Time saving for those who able to use the HOV lanes likely to offset disbenefits to SOVs.

Community impacts

Faster traffic.

Environmental damage

/ Some reduction in traffic, but offset by increased congestion on SOV lanes.

Poor accessibility

By reducing public transport journey times and increasing its reliability and favouring low-car-ownership households.

Social or geographic disadvantage

By improving access.

Accidents

Increased speeds and conflicts between HOV and LOV may cause accident risk, pedestrians may also have more difficulties crossings.

Economic growth

By improving access, but impacts small.
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Appropriate contexts 

It was suggested that HOV lanes are most effective at reducing car use in major urban areas with large employment centres, heavy congestion and complementary policies where public transport provides time savings of at least 5 to 10 minutes per trip (Turnbull, 2001; Pratt,1999). Similar conclusions were also supported in ICARO (2000).

Appropriate area-types

Area type

Suitability

 

City centre

On radial arterial to city centres

Dense inner suburb

From these suburbs to employment centres

Medium density outer suburb

 

Less dense outer suburb

 

District centre

 

Corridor

 

Small town

Tourist town

 
= Least suitable area type = Most suitable area type

Adverse side effects

When an HOV lane is not combined with complementary measures such as travel plans, car sharing initiatives, public transport improvements, it might result in under-utilisation in road capacity and therefore cause extra delays to general purpose lane users.

In contrast, when time saving are high, it can induce trips from parallel routes, induce additional trips or shifts from other times. It may also cause abstraction of public transport users to join SOV drivers to enable them to use the HOV lane. 

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