5.6Corridor Length
Time is the longest distance between two places.Tennessee Williams, dramatist, 1911–1983
The basis for the cost-benefit analysis of corridor length is typically the time savings generated by the exclusive busway. Once the exclusive busway no longer provides a net time savings benefit in comparison to the construction costs, then the point has been reached when the exclusive busway is no longer cost justifiable. As the number of customers falls with the distance from the city center, the total time savings benefit is reduced. Further, since congestion levels will also likely fall with distance from the city center, the travel-time advantage of an exclusive busway will likewise fall. Table 5.3 provides an example of a cost and benefit analysis plotted against a corridor’s length.
Of course, this time savings benefit will tend to increase as congestion worsens over time. Since a BRT system is likely to last a long time, it is standard practice to roughly estimate the likely congestion along the corridor in the next ten to twenty years rather than simply assuming that current congestion conditions will prevail long into the future.
Table 5.2Cost-benefit analysis of corridor length
| Corridor segment | Length of segment (km) | Demand along segment (x 1000) | Time savings (minutes) | Cost | Benefit | Benefit / cost ratio (B / C) | ||
|---|---|---|---|---|---|---|---|---|
| Total | / km | Total | / km | / km | ||||
| A | 3 | 13 | 6 | 2.00 | 5 | 1.67 | 26.00 | 15.60 |
| B | 2 | 12 | 4 | 2.00 | 4 | 2.00 | 24.00 | 12.00 |
| C | 1.5 | 13 | 5 | 3.33 | 3 | 2.00 | 43.33 | 21.67 |
| D | 3 | 11 | 4 | 1.33 | 4 | 1.33 | 14.67 | 11.00 |
| E | 1.8 | 9 | 1.2 | 0.67 | 2 | 1.11 | 6.00 | 5.40 |
| F | 3.1 | 7.5 | 2.5 | 0.81 | 4 | 1.29 | 6.05 | 4.69 |
| G | 2.3 | 6 | 0.5 | 0.22 | 3 | 1.30 | 1.30 | 1.00 |
| H | 1.5 | 4.5 | 0.6 | 0.40 | 2 | 1.33 | 1.80 | 1.35 |
| I | 3.1 | 3 | 1 | 0.32 | 5 | 1.61 | 0.97 | 0.60 |
| J | 1.9 | 2.2 | 0.2 | 0.11 | 3 | 1.58 | 0.23 | 0.15 |
In the example given in Table 5.1, the corridor would end after segment “H” if the decision was based only on benefit to cost considerations. After segment “H,” the benefit to cost ratio falls below a value of one, meaning that the costs of extending the exclusive busway corridor outweigh the time savings benefits.
5.6.1Where to Build Infrastructure Versus Where to Run BRT Services
Modern thinking in BRT planning has evolved to separate BRT infrastructure from BRT services in such a way that BRT services may operate both on- and off-corridor in a way that optimizes customer benefits versus infrastructure cost. Therefore, in the sections above, “BRT corridor” refers directly to the infrastructure built on a segment of road, rather than to the services that are needed.
Once a corridor has been selected, it is important to make an informed judgment regarding where to design BRT infrastructure and for how long of a stretch. This is best done by graphing the demand distribution and speeds during the peak hour, and selecting the location with both the highest demand and lowest speeds. Per the definition of BRT, the selected corridor must be at least 3 kilometers.
Building BRT infrastructure on the segment of roadway along the corridor with the highest demand means that infrastructure investment will yield the greatest benefits. Oftentimes, however, the sections of a corridor with the highest demand are precisely the sections where politicians are less willing to propose BRT infrastructure, as those sections often face more constraints. As a result, BRT infrastructure often stops just before the segment where it is needed most. The BRT Standard (2014) awards maximum points to corridors that include the highest quality of BRT infrastructure on the highest demand segment. This often means extending the BRT directly into the city center. For other corridors that do not come near the city center, this may simply mean the area with higher demand than the rest of the city.
Once the location for BRT infrastructure has been selected, one must consider what to do beyond the infrastructure. Many cities propose lower-quality bus treatments beyond the infrastructure. Generally, however, it is preferable to allow BRT services to simply enter mixed traffic beyond the infrastructure. This sends a clear signal to the public that there is a difference between BRT and everything else, and leaves open the possibility of building out the rest of the corridor as full BRT at a later date. If lower-quality bus treatments are implemented beyond the BRT infrastructure, it is less likely that they will ever be upgraded to full BRT.
Finally, it is possible to design BRT services to extend beyond the BRT infrastructure into many parts of the city. This expands the catchment area of the BRT to many more beneficiaries than simply a service that directly matches the infrastructure. It also provides an opportunity to bring new BRT services to sections of the city where no bus services previously existed but where stakeholders wished to see a BRT corridor. That is, in some cases, during the corridor selection process, some selection of stakeholders may advocate for a corridor with no preexisting bus demand. It is unlikely that such a corridor will make it to the list of top corridors for BRT implementation. However, if the requested corridor is located near the corridor ultimately selected, it may be reasonable to run a service into that area to begin to grow demand for future BRT infrastructure in that location, as well as to demonstrate to stakeholders that such an area will be a beneficiary of BRT.
The next chapter covers how to develop and optimize a BRT service plan. But it is worth noting here that a BRT corridor with multiple services receives maximum points on The BRT Standard (2014).