Eric identifies an important issue for high-frequency grids, like those of Vancouver, Los Angeles, Chicago, Portland's eastside, etc … The short diagonal trip may be not much faster than walking. Here's how he describes it, complete with clever 1980s-style computer graphics:
When discussing grids, it is important to think about trips like the following:
Start
|
| (1/4 mile)
|
|********(1 mile)************
A—————————-B
*****************************|
*****************************|
*****************************| (1 mile)
*****************************|
*****************************|
*****************************|
*****************************|
*****************************C—–Finish
*****************************(1/4 mile)***(please ignore the '*' – they exist only to make the vertical lines go in the proper place).
The grid's approach to this trip would be to walk to A, then take a bus to B, then take another bus to C, then walk to the end. However, since each bus segment is so short, even with frequent service, the waiting time still becomes a huge deal.
For example, if we assume that the buses each run every 15 minutes the expected travel time might look something like this:
Time =
5 minutes (walk to A)
+ (0-15) minutes (wait)
+ (5-10) minutes (ride bus to B)
+ (0-15) minutes (wait)
+ (5-10) minutes (ride bus C)
+ 5 minutes (walk to destination)
= (20-60) minutesThe average 40 minute travel time is just 3.75 miles per hour, equivalent to a brisk walk, while the worst-case travel time is a mere 2.5 miles per hour, equivalent to a slow walk.
With the slow speeds and huge travel-time uncertainty in the above calculations, before you even consider the possibility of bunching leading to 20-30 minute waits, if the goal is simply to get to the destination quickly and reliably, transit can't even compete with walking, let along with driving.
This relegates the use of transit for these trips to people can't walk or bike and also can't afford to drive or spend $10 on a taxi ride.
Trips like these are not edge cases. I make trips like this quite frequently. Usually, I end up either biking or jogging the entire way or walking half way and taking a one-seat ride for the other half.
My personal opinion is not that the poor handling of such trips is a failure of transit, but rather that there are certain types of trips that transit is optimized for and short L-shaped trips isn't one of them. Short L-shaped trips are simply better accomplished by some other means, such as walking, jogging, skateboarding, bicycling, or even riding a taxi, while longer trips, especially trips in a straight line, allow transit to work more efficiently.
If anybody else has opinions on the matter, I look forward to hearing them!
Eric's point connects to a bunch of intersting issues:
- What other solution is there? Look at the overall mobility outcome from straight, fast, frequent lines in a grid pattern, and ask: OK, yes, this is not so convenient for the short diagonal, but what exactly can or should we do about that? In some cities, notably Los Angeles, you'll often find little circulators that serve some of these diagonals where there is a specific market for them, such as a link between two key local activity centers. But these are always going to be specialized because they are so much less efficient than the main grid lines.
- Note how much this outcome depends on the overall quality of the straight grid lines. Eric assumes they're pretty poor. In fact, the diagonal grid trip usually has a choice of two L-shaped paths ("over and down", or "down and over") so there's an opportunity to choose the better of these two, which will the the one that uses more frequent or faster services.
- Eric's assumptions are for a standard local-stop grid. Frequencies are assumed to be never better than 15 minutes, and travel speed, for example, is 5-10 min to go a mile, an average speed of only 6-12 mi/hr. Some urban lines are down in this range, but such performance should be considered a problem in urgent need of attention. Stop spacing and a range of minor infrastructure can have large impacts, and will yield benefits that are much greater than you'll get by dissipating your service over countless little diagonal shuttles. So there's much that can be done to improve the short-diagonal problem simply by focusing improvements on the grid lines.
In short, I agree with Eric's conclusion. Because I tend to live in urban places where most of my trips are short, I encounter the short diagonal problem all the time. It's a drag, but I deal with it because I'm pretty sure that it's geometrically impossible to "solve," except by undermining far larger benefits of a network that serves the whole city, and that moves fast enough to compete with cars, not with walking.