Widening or Bus Rapid Transit on a 22 m Arterial
An arterial corridor in a city of 900,000 carries 18,000 passengers per hour per direction at peak in mixed traffic: two general lanes each way, a 22 m right-of-way, and a 3.2 km length. Average bus speed is 11 km/h; 40% of motorized trips on the corridor are under 3 km. Pedestrian crossings are 400 m apart, and crash data show 14 pedestrian injuries in two years. The roads department proposes widening to three lanes each way, which requires removing 2.5 m of sidewalk on each side and 60 mature trees. A transport consultant proposes a median BRT with 1.5 lanes per direction for general traffic, 26 m stations, and signal priority. Peak car occupancy is 1.3. The mayor wants a decision before the next budget cycle.
1. Assess whether widening can solve the peak problem, using the numbers in the setup.
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Widening cannot solve the peak. The corridor carries 18,000 persons per hour per direction in mixed traffic. Adding one general lane each way adds roughly 1,800-2,000 vehicles per hour per lane at ideal conditions, or about 2,300-2,600 persons at 1.3 occupancy. That is a small fraction of 18,000, and it is optimistic because the corridor already has intersections, crossings, and only 22 m of space.
The 40% of trips under 3 km are the key. A large share of car trips are short and could shift to walking, cycling, or bus if those are made attractive. Widening removes 2.5 m of sidewalk on each side and 60 mature trees, which worsens pedestrian safety and comfort and induces additional car travel. The 14 pedestrian injuries in two years point to a design and speed problem, not a capacity problem. The roads department is counting vehicles, not people.
2. Compare BRT and widening on person throughput, induced demand, safety, and cost.
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Person throughput: a median BRT with 26 m stations and signal priority can move roughly 8,000-20,000 persons per hour per direction depending on bus size and headway. Even a conservative 12,000 exceeds the incremental capacity of one extra general lane. Widening moves more cars but fewer people per meter of right-of-way.
Induced demand: extra car capacity fills over time, so the peak returns. BRT with priority protects bus speed and reliability and can be upgraded.
Safety: BRT with median stations and signalized crossings reduces conflicts. Widening with narrower sidewalks increases pedestrian exposure.
Cost: widening requires utility relocation, tree loss, and land. BRT requires stations, buses, and repaving but uses the same 22 m. The fair comparison is person-delay and safety, not vehicle level of service.
3. What would you recommend, and what design conditions would you attach?
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Recommend the BRT, with conditions.
- Keep 1.5 general lanes per direction only if a traffic model shows acceptable local access; otherwise use one general lane plus turn pockets.
- Maintain at least 3 m clear sidewalks on both sides and plant replacement trees.
- Add crossings every 200-250 m, especially near schools and markets.
- Provide level boarding, shelter, and secure bicycle parking at stations.
- Use camera enforcement of the bus lane and a defined freight and delivery window.
Before construction, publish a monitoring plan: bus speed (target 20-25 km/h), ridership, pedestrian injuries, sidewalk width, and peak car delay. If the corridor's through traffic is largely external, add a parallel route or a cordon charge rather than taking right-of-way from pedestrians. Frame the decision as a person-throughput and safety project, not a war on cars.