Designing Bus Lines for New Urban Communities

By William Lieberman, AICP

To achieve the full benefits of life in a new urban community, residents need travel alternatives in order to be free from full-time automobile dependency. Such communities should of course be designed to make walking and cycling easy and convenient, but what about public transit?

In the majority of new urban and suburban developments, transit comes into its own as a way of linking the community with the rest of the metropolitan area. Trips to work lend themselves to transit and are responsible for the largest single category of transit travel. For many people, work trips occur with great regularity: to and from the same end points, five days a week, at approximately the same times each day. Trips to and from school are next in volume, also due to their regularity, and to the fact that many students can't drive or don't have access to a car.

Designing an effective transit system-or, more likely, just a single line to serve a new community-requires a thorough understanding of the wants and needs of the residents and workers in that community. Unfortunately, this information can only be based upon speculation until people actually move in. Then it may be too late, since those people may soon become accustomed to the same auto-centric way of life they had in their previous locale. Nonetheless, there are some rules of thumb that can ensure that a new transit line has the attributes that are important to the more demanding market segments. Here are a few:

1. Routes should be direct, following a relatively straight path of travel. Through riders get impatient with the time delay of deviations off the main path. Such deviations will sometimes be necessary to serve a major destination (see No. 2) but they should be few and far between on any single transit route.

2. Major destinations (such as large workplaces, shops, schools and medical facilities) should be located within an easy walk of the transit line. The practical walking distance from a bus stop is ¼ mile, and for a rail stop, 1/3 to ½ mile. However, these rules of thumb are only for residential areas. The more important the destination, the closer it should be located to a stop. For example, a major hospital would not be well served at the very edge of the ¼ mile catchment area of a local bus line and probably should have a stop at its front door. If the hospital is already in place, the bus route may have to divert to serve it. If the hospital is not yet built, consider a location and site placement that will minimize diversions from the main bus path.

3. Some streets may not be suitable for full-sized buses because of their narrowness. It's best to anticipate during the planning stage where buses will travel so that the streets involved can be designed accordingly. It is not recommended to operate buses on streets that are so narrow that one vehicle must pull over to let an oncoming vehicle pass.

A minimum reasonable lane width for full-size buses is 10 feet, with 12 feet being desirable. Therefore, a two-lane street with parking on both sides would be 36 feet curb-to-curb minimum and 40 feet desirable. Small buses may reduce this need, but such buses may not be appropriate for the volume of riders anticipated, or they may not be operated by the transit agency that will provide the service.

Municipal officials are often concerned that small curb radii (i.e., sharp corners) will hamper bus movement. What is frequently forgotten is that new urban streets are usually designed with on-street parking. Therefore, turns are started some distance out from the curb. Charles Brewer of Green Street Properties has shown that, on streets with parallel parking on both sides, a 5-foot curb radius is sufficient for a full size bus. Brewer's Law states: "For every foot that you increase the starting/ending distance from the curb, the required curb radius is reduced by 3.415 feet (equal to 1.414/.414)."

The ideal turning radius avoids the encroachment of a vehicle into the oncoming lane of the street that vehicle is turning into. However, if traffic volumes are very low on that street, the chances of a bus encountering a vehicle in the oncoming lane are low as well, making this a permissible practice on occasion.

4. The span of service (times of the first and last trip each day) and frequency are very important factors in attracting auto users to public transportation. Regarding span of service, the hours of 6:00 am to 7:00 pm, Monday - Saturday are a suggested minimum; 5:00 am to midnight every day would be desirable.

It's okay to start out with service only during the peak hours for a line serving mainly workers and students. Routes that are designed purely as peak-hour commuter runs would be more likely to operate 5:00 am to 8:00 am and 3:00 pm to 6:00 pm, Monday - Friday.

Frequency is much harder to specify since, of course, the more frequent, the better. Thirty 30 minutes is the suggested minimum in most cases (as opposed to the 1 hour frequency often used by transit systems). A more desirable frequency of at least 15 minutes (and less, if patronage demands) should be sought to attract the more demanding market segments.

The big problem with both long spans of service and short frequencies is that they cost more money. Municipalities are loath to spend any more than they have to on public transportation. As a result, they offer the minimums and only attract patronage that seems to fit those levels. They never break through to higher ridership because the services they offer don't have the attributes that the more demanding travelers want.

5. Transfers can make or break transit ridership. In many cases, travelers won't be able to access their destination on a single route, so the process of transferring to a second route should be fast, convenient and comfortable. If service is offered at less than 10- to15-minute intervals on one or both routes, then transfer times should be coordinated whenever possible. Even then, the stops involved should be equipped with benches, illuminated shelters, and posted timetables -- or better yet, real-time information displays.

Those concerned with the development of new communities quickly discover that starting a brand new transit route can be a time-consuming endeavor that requires prior experience. If the community is located in or near the service area of an existing transit agency, that agency should be approached to initiate a service or to extend an existing line nearby. These rules of thumb can assist the community in negotiating the kind of service that best fits its needs.

William Lieberman, AICP, is a transit planning consultant based in San Diego, Calif.