Buses running on city streets can get stuck in traffic, move slow as molasses, and bunch up. New, dedicated infrastructure is hard to fund and build. But could we use freeways to provide express bus service?


A “bus pad” in action in San Rafael, California. Photo from Google Street View.




Our freeways provide ready-made, grade-separated, fast infrastructure that could be redeemed for express buses and regular bus service, too. There are three ways to approach the freeway bus system. One is the bus pad, which places the stops along slip lanes at each interchange. Golden Gate Transit (GGT), in the San Francisco Bay Area, uses this system extensively in Marin County.

Another is the bus expressway, which mixes buses with other high-occupancy traffic and places stops either at overpasses or in the median. King County Transit in the Seattle area uses this system. A third way is the center-running bus rapid transit system, which dedicates lanes exclusively to buses.

We’ll look at each of these types, but today, let’s start with the bus pad. Even though they force buses to take the slow lane, using bus pads results in a service that flies compared to buses on city streets.


Map of bus service along Highway 101 by the author. Click for a larger version.


GGT’s system is something of a historical accident. When Highway 101 was being built, someone realized this would lock out those who used to take buses along the old Redwood Highway, which 101 would replace. So engineers added bus-only slip lanes and a bus stop at each exit, giving Marin County the closest thing to bus rapid transit in the Bay Area.

Despite running on a freeway, the buses can be slow. The average speed, excluding time spent on surface streets, rarely peaks above 30 miles per hour. Local buses average 19 miles per hour between Novato and the Spencer Avenue bus pad, a distance of 20 miles.

Skip-stop express buses do the same run at 30 miles per hour, though they top out at 48 miles per hour when traffic is particularly clear. Both locals and express buses spend 7 minutes laying over at transit centers along the route, which cuts a few miles per hour from their average.


A “bus pad” in Corte Madera, California. Photo from Google Street View.


This may not seem too rapid at first, but in the world of public transit this is actually quite speedy. Metro averages 33 miles per hour, and New York’s subway only averages 18.6. Compared to the often-miserable speeds of buses on city streets, which rarely top 10 miles per hour, this is rapid transit.

But unlike rapid transit, most of the infrastructure is already built. All one needs is a safe way for a bus to service a bus pad at a preexisting interchange or exit, and a safe way for riders to get to the pad. Diamond interchanges are easiest to service, as a bus just needs to exit the freeway, pick up passengers at the pad, then continue forward to reenter. Others, like cloverleaf interchanges, require a bit more but typically there is enough space to accommodate the bus pad’s slip lane and stop.


Bus pads in a diamond interchange. Photo from Google Maps edited by the author.


Though cheap and fast, the bus pad has a number of downsides. Foremost, the passenger has to wait at the edge of a freeway. It’s hot, polluted, loud, windy, dry, and terrifically unpleasant. The walk to the bus pad might not be so attractive, either, as freeways are notorious for turning their neighborhoods into moonscapes.

Transfers can be a pain, too. One bus pad in Marin requires a quarter-mile walk through that moonscape and across an overpass to transfer from the freeway to surface streets.

Freeways are not conducive to transit-oriented development, either, which would otherwise be a natural outgrowth of a high-speed rapid bus line running through the city. Though this is a problem bus pads share with other busway designs, the unpleasant and difficult transfers further limit the scope and attractiveness of transit-oriented design.


Bus pads in a cloverleaf interchange. Photo from Google Maps edited by the author.


Finally, buses serving bus pads don’t make use of HOV lanes, as they need to stay in the far-right lanes. That means they can still get stuck in traffic and delayed. Shoulder bus-only lanes can help, but it still exposes them to traffic at exits. At commute time, this can be especially frustrating for riders.

One way to limit these problems is to eliminate the slip lane and place the bus stop at the top of the off-ramp. Buses would exit the freeway, service the stop, then jump back on. While this exposes the bus to stoplights, if a bus-only shoulder continues along the exit, the bus could still bypass congestion and serve much more comfortable and accessible stops.

Under this structure, transfers to surface routes could be as close as the adjacent corner. If coupled with a bus-only shoulder that extends along the ramps, buses could bypass the traffic entirely.

Unfortunately, many of DC’s freeway interchanges are tortured things, squeezed into odd geometries and designed to allow the most options for exiting vehicles. They may not have space for a slip lane and bus stop, or may not have an easy way for an exiting bus to immediately return to the freeway. For areas with the most potential, such as the Southwest Freeway and I-66, interchanges would need to be completely re-engineered.

Moving the stops to the middle of the freeway while keeping buses mixed with traffic offers a way around that problem. It also allows them to take advantage of high-occupancy lanes, improving reliability and speed. We’ll talk about this design, the bus expressway, next time.