The idea of BRT was put forward to use buses in order to imitate light rail services. However, in North America, two factors have so far limited the full development of this concept: 1) the inadequate deployment of several projects due to an approach favouring lower costs over high quality, efficient solutions; and 2) limitations in bus capacity that make it difficult for them to provide the same level of service as rail solutions.

But first, let’s adequately define the notion of BRT because the term has been much abused. According to the official industry standard, BRT is:^1,2

• A high-quality bus-based transit system that delivers fast, comfortable, and cost-effective services at metro-level capacities. It does this through the provision of dedicated lanes, with busways and iconic stations typically aligned to the center of the road, off-board fare collection, and fast and frequent operations.

The industry uses a scoring system to define several deployment levels ranging from basic to bronze, silver and gold.^1,2 In Canada and the United-States, no gold level project has ever been commissioned. Most are classified bronze or basic. There are two silver projects in the U-S. It should be noted that many projects purporting to be BRTs do not meet the minimum standards of the basic level. Much more than a simple improvement in bus services, a true BRT service provides infrastructure investments and an operating model that promote speed and efficiency. In other words, a BRT system encompasses three pillars: vehicles, infrastructure and efficient operations.

As part of the ongoing European eBRT 2030 project, the UITP has identified five fundamental criteria to characterize and benchmark a BRT system⁷:

• Right-of-way (vehicle priority infrastructure)
• Frequency and service span
• Stations convenience and accessibility
• Branding and communications
• Operational performance (speed and travel time)

Two factors limit BRT services: the service capability of the vehicles themselves and, by extension, the possibility of commissioning a sufficient number of vehicles during a given period. It is these discriminatory factors that justify choosing rail over BRT.

A 12m long North-American bus can accommodate about 80 passengers. An 18m articulated bus can take approximately 130 passengers, while a 24m long bi-articulated bus (not yet deployed in North America) can carry up to 180. Data that sometimes indicate much higher theoretical numbers are not practically realistic in the North American context. Comparatively, trams measuring 25m to 50m in length have a typical passenger capacity of 170 to 350 passengers. For their part, LRT vehicles can accommodate up to 600 passengers or more.

And now, the crux of the matter. The cost of drivers typically represents 50% of the operating budget of a public transit authority bus network. It may seem easy to simply double the network's capacity by doubling the number of buses in service, but the impact on the operating budget makes this generally impossible and uneconomic. Most public transit networks are under pressure to maintain a balanced budget and passenger fares make up only a small part of their financing. Consequently, added revenues derived from increased ridership do not cover the increase in operating costs.

This is one of the important factors explaining why cities wishing to increase their transit services favour light rail systems, and especially trams. Since higher government levels shoulder the high capital costs of building rail infrastructure through specific financing instruments, municipal authorities take on only direct operating expenses, which remain reasonable. The current financing model therefore significantly influences which projects are prioritized by elected municipal officials.