The one-way-only Huron Transit Station near the University of Minnesota. Literally a half-hearted attempt at using freeways for bus service. [View Larger Map]
As I first started exploring Metro Transit's bus network in college, I was struck by how much freeway mileage in the Twin Cities doesn't carry any transit service. Having grown up near Rochester and typically only visiting or driving through the metro area a few times per year, my mental map was mostly built up of Interstates and other major highways, so many of the landmarks I wanted to visit would require long, slow trips on urban local bus routes, and many destinations were simply out of reach with the time I had available. That might not have been the case if there were more freeway-running routes that had more symmetrical schedules throughout the day.
There is an extensive network of express routes for ferrying suburban workers and students into our twin downtowns and the University of Minnesota—and some highways (such as I-35W near Lake Street) do see buses going by a couple times per minute at peak times. But, with a few notable exceptions, express routes tend to run as if they were local routes for a short distance to pick up riders out in the suburbs, then go non-stop to a major core-area destination. There are some places where express buses stop partway along highway, but even then, it may only be a flag stop for riders getting off or the bus may skip past the stop on certain runs. The inconsistencies can induce nightmares for first-time passengers.
Good transit lines, on the other hand, make regularly-spaced stops. The spacing can vary depending on how much speed is desired, but they really gain strength from connecting a variety of different locations rather than focusing on bunch of origins clumped together at one end and a cluster of destinations at the other. The number of practical trip combinations is usually much higher and attracts more riders.
The core reason why express bus routes avoid stopping along the way comes down to the defining feature of a freeway: They're made for non-stop travel by vehicles making point-to-point trips—they're not made for buses picking people up and dropping them off along the way. Continuous flow is the goal with a freeway, and the only places where a vehicle is supposed to stop are at the ends of off-ramps.
A freeway corridor is an assault on the senses for any pedestrian, with noise, pollution, and the risk of being run over on nearby streets by drivers who haven't quite gotten their mind out of "freeway mode" yet. So while it's pretty easy to put bus stops right at diamond interchanges, they can be very unpleasant places to be.
Diamond interchanges are some of the best candidates for bus stops along freeways, since buses can pull off the highway, hit a stop, and then get right back on. However, many interchanges these days use different designs that don't allow buses to get off and right back on. In some parts of the Twin Cities, there are some bus routes which get off the highway and then loop around on local streets and special service roads to access nearby transit stations, but that drastically reduces the average speed of travel for passengers.
Along the nearly-opened Red Line in the south metro, the first station south of the Mall of America is the Cedar Grove Transit Station. It's next to the 65-mph Minnesota State Highway 77 (also known as Cedar Avenue), but accessing the station requires looping back from the junction with Diffley Road 3/4 of a mile away. Stoplights and lower speeds on surface streets mean that reaching the station adds around 6 minutes to the travel time. This is along a route that's only going to operate over a 9-mile route when it opens (expected to grow to 12 or 15 miles eventually).
So why didn't planners simply decide to put in a station right at the Diffley Road junction? I don't know the definitive answer, but it's worth pointing out that the distance between the northbound and southbound on-/off-ramps is around 900 feet, and the distance between the nearest frontage roads on either side of the highway is almost twice that (about 1760 feet). The sheer scale of suburban and rural freeway junctions creates a huge barrier—most transit bus riders are only willing to walk about 1/4-mile (1320 feet) on each end of a trip, meaning that the pedestrian "shed" for such a stop would be completely devoid of any potential customers. That's in contrast to junctions along urban corridors like I-94 in western Saint Paul and I-35W in south Minneapolis, where the distance between eastbound/westbound or northbound/southbound ramps is about 330 feet.
This isn't just a problem for metro-area transit buses, though—intercity routes also have similar problems. While Interstate highways sliced right through residential areas of major cities across the U.S., smaller towns were usually bypassed instead. Places where the main drag was once a state or U.S. highway often saw the new freeway entrance built a mile or two away. While the "highwayless town" does have certain advantages, it did mean that bus routes which once hopped along from one small town to the next (often attempting to mimic old rail lines that had also gone right through town centers) had to shift to picking people up and dropping them off out on the fringes.
Official stops for services from Jefferson Lines, Greyhound, and other bus lines are typically located as close to the highway as possible in the parking lots of gas stations, McDonald's restaurants, and so on. Windswept, empty places without much shelter (at least once the convenience store or restaurant manager tires of letting passengers hang out inside).
Other problems with connectivity also plague freeway-borne bus routes. In south Minneapolis, the 46th Street station on Interstate 35W is skipped by many buses that run east-west along MN-62, simply because it's difficult to maneuver southbound buses across 3 or 4 lanes of traffic in the 1-mile distance between the station and the MN-62 exit. The first true freeway BRT station in the Twin Cities is underutilized as a result.
When done right, freeways are engineering marvels. They dramatically increased mobility across the U.S. following World War II, but they've been lacking crucial design elements to make them proper conduits for mass transit as well as cars and trucks. These highways could have been built differently, with better options for bus stops and stations, and possibly dedicated ramps and busways for reaching city and town centers more rapidly than what would be possible by car.
Are there opportunities to flip this equation around? The Twin Cities does have the country's most extensive network of bus-only shoulders to bypass congestion on freeways (as well as some surface highways), but most of that mileage only improves travel times for suburban commuters and does little to help urban dwellers who dominate transit ridership in the region. In some cases, buses on freeways won't provide any better access than urban or suburban local routes, but it's a ready-made network of high-speed, grade-separated infrastructure that shouldn't be ignored as we face the challenges of the 21st century.