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When Is a Bus Lane Warranted?

Efficient and equitable urban roadway management favors higher value trips and more space-efficient modes over lower-value trips and space-intensive modes. This can justify bus lane networks in most major cities.

Todd Litman | July 17, 2015, 7am PDT
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Next month I will present a paper at the Thredbo International Conference on Land Passenger Transportation titled, When is a Bus Lane Warranted? It examines where dedicated bus lanes are justified based on economic efficiency and social equity principles. This is an important and timely issue for cities around the world. 

Cities are, by definition, places where many people and activities locate close together, so urban space is always scarce and valuable. As a result, efficient and equitable urban roadway management favors higher value trips and more space-efficient modes over lower-value trips and space-intensive modes. 

Bus lanes increase urban transport system efficiency by favoring space-efficient travel.

Bus lanes are a practical way to do this. They can carry an order of magnitude more people than a general traffic lane (see image below), and help achieve social equity objectives by ensuring that non-drivers are able to use a fair share of public road space, and helping physically, economically and socially disadvantaged people access economic opportunities. As Enrique Penalosa explains in this TED Talkbus priority lanes, represent democracy in action by allocating public road space to poor as well as affluent residents.

Although a single bus lane may seem to provide only modest direct benefits, an integrated bus lane network implemented with other pro-transit policies can be the fastest and most cost-effective way of creating more multimodal cities where travellers choose the most efficient mode for each trip: walking and cycling for local errands, public transit when travelling on busy corridors, and driving only when it is most efficient overall, considering all impacts. Unfortunately, current transportation evaluation methods are unsuited to such analysis. Conventional traffic models tend to underestimate the impacts that high quality public transit and transit-oriented development have on automobile ownership and use, and conventional economic evaluation tends to overlook or undervalue many resulting benefits such as parking cost savings, increased traffic safety, and reduced chauffeuring burdens. We need better tools to help decision-makers decide when to implement bus lanes. The following table lists various types of benefits and costs that should be considered when evaluating public transit improvements, including dedicated bus lanes.

Public Transit Benefits and Costs


Improved Transit  Service

Increased Transit Travel

Reduced Automobile Travel

Transit-Oriented Development (TOD)



Service Quality        (speed, reliability, comfort, safety, etc.)

Transit Ridership (passenger-miles or mode share)

Automobile Travel Reductions

Portion of Development With TOD Design Features


Improved transit operating efficiency

Improved bus passenger travel speed and reliability

Option value (the value of having options that may sometime be useful)

Equity benefits (since existing users tend to be disadvantaged)

Direct benefits to new users

Increased fare revenue

Increased public fitness and health (by stimulating more walking or cycling trips)

Reduced traffic and parking congestion, and resulting facility cost savings

Consumer savings

Reduced chauffeuring burdens

Increased traffic safety

Energy conservation

Air and noise pollution reductions

Additional vehicle travel reductions (“leverage effects”)

Improved accessibility, particularly for non-drivers

More efficient development (reduced infrastructure costs)

Farmland and habitat preservation


Higher construction and enforcement costs

Increased congestion in other lanes

More crowded buses

Reduced automobile business activity

Various problems associated with denser development

Bus lanes can have various benefits and costs that should be considered in evaluation. Some of these impacts are indirect and long-term, so their evaluation requires predictive modeling of travel and land development. 

An ideal urban transit network provides high-quality service within a ten-minute walk of most homes, jobs and services, which requires a gird of grade-separated rail or bus lines spaced no more than a kilometer apart. Many cities are starting to implement bus lanes and other bus priority strategies. For example, although London is most famous for its subway system and congestion pricing, improving and expanding its bus lane network is a critical component of improving overall transit service quality and regional transport system efficiency. But there is far more potential.

In many situations, bus lane development will increase general traffic lane congestion in the short term, although this will decline over time as more travellers take advantage of the improved transit service, particularly if implemented with other transit-encouragement strategies. Comprehensive evaluation weighs this incremental motorist delay against transit travel time savings (including reduced bus operation and passenger travel time costs), reductions in automobile external costs including downstream traffic and parking congestion, accidents and pollution emissions, the social equity value of improving mobility for non-drivers, plus the strategic value of creating more multimodal transportation systems.

London bus lanes

I found no simple warrants that define when bus lanes are justifiedMy analysis suggests that bus lanes are generally warranted where, after all economically justified pro-transit policies are implemented, they would attract more than 800 peak-hour passengers (about 20 buses) on surface streets or 1,800 peak-hour passengers (about 30 buses) on grade-separated highways, since those lanes carry more passengers than a general traffic lane, and so save total travel time, and by reducing urban-peak automobile travel, they provide additional indirect benefits, including reducing downstream congestion, providing road and parking facility cost savings, and by reducing traffic accidents and pollution emissions. As a result, more comprehensive evaluation can justify extensive bus lane networks in most cities, particularly rapidly-growing cities in developing countries.

What do you think? Are there other impacts and objectives to consider? Are there better ways to determine when bus lanes are justified? Are there better ways to communicate the value of high quality transit and pro-transit policies to decision-makers and the general public?

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