It's a river, not a road
How to decide if it needs to be an integrated street or a sheltered road
Last week we talked about how both low speed streets and higher speed roadways are generally safe, but stroads aren’t. The metaphor of a river helps explain why and can help policy makers and designers decide how the crossings should be handled.
To recap: In a dense urban area where things are tight and the flow is slow, there’s no real problem crossing. Pedestrians get seen. Drivers don’t mind stopping. Everyone watches out for everyone else. In the Netherlands, a stop sign for bikes is seen as a design failure. In their world, if you have to dictate who gets priority, they haven’t designed it well because users that are going about the same speed can negotiate with each other eye to eye without our help.
Higher speed roads are safe too, but not safe to cross without help. Pedestrians (and most cyclists) know better than to try. It’s pretty obvious to the engineering community too. Pedestrian treatments are given in the intersections. Locations where pedestrians frequently cross are given extra design care—and sometimes their own signal.
Here’s the problem: in the middle it’s easy to assume it’s fine when it’s not—for both the pedestrians and designers. If the traffic flow is going much more than about 20 mph, pedestrians only get seen about half the time. Those are not good odds. As the flow creeps up into the 30’s and 40’s, crash survival rates are low, drivers are over-driving their ability to negotiate eye to eye (like overdriving your headlights), and their reaction times may only be enough to cripple a person instead of kill them. The same crash at night becomes a fatality.
Crossings when the flow is faster
If you’re in an area where vulnerable users need to be sheltered, designers will often need to give them a ford to cross, because they are going to try. If it’s dangerous enough, you may need to give them a bridge or a tunnel and railing to keep them from falling in—accidentally, mind you (not!)
Emergency management directors will tell people not to try to cross a flooded street because you don’t know how fast it’s going or what might be under the water. People ignore them because they need to get somewhere—often to their peril. Out west, a summer thunderstorm can change a canyon from fordable to flooded in minutes. Our signalized roadways can mimic this. It’s like the water gets dammed up every few minutes, making it look safe, but cars turning from the side street can cause tragedies—especially if the road or turn radius are wide, making the driver feel like they can get back up to speed quickly.
Roadway designers assume that pedestrians will only cross at intersections or crosswalks, where it’s legal to do the crossings—but that’s a bad assumption. Pedestrians will often risk crossing in places they know aren’t ideal because the spacing between crossings is wide, the desire lines are attractive, or the flow seems manageable. If you take the design of shopping malls as evidence, you’ll probably see people crossing mid-block if the block is approaching 600 feet long. A pair of attractive locations on opposite sides of the road may lure folks to cross even in shorter blocks. For instance, if the parking lot for your library has a sidewalk access that lines up with the entrance in front of the building, people are going to take that as a signal that crossing there is intended, even if they’re crossing a 4-lane road—and it may end up costing someone their life.
Hints from Fording Advice for Hikers
On hiking trails, fording a river is something you may need to do, but there is concrete guidance for when that is safe and when it’s not. Here’s what I found from the National Park Service:
“The swifter the water the shallower it has to be to cross safely. If you cannot walk as fast as a stick is floating downstream, it is probably not a safe spot to cross.”
Takeaway: if the flow is fast—even if it’s intermittent—it’s risky. Wading across fast moving ankle deep water may work. If the flow rate is really low, like on a neighborhood street, it’s probably fine, even when drivers are going faster than we want them to. The more volume there is, the more dangerous it gets. As a roadway designer, crossing a fast flow is likely to be dangerous. Make them a ford.
“Avoid crossing through water deeper than your knees if possible. The only time to wade through deeper water is when you locate a flat pool with little or no current.”
Takeaway: High volume roadways need crossings where the current comes to a complete stop or at least a dramatic slowing before people can safely cross. That may mean an intersection. That may mean a dedicated crosswalk where the blocks are long and the attractors have lots of pedestrian visitors.
“If there is an island or sandbar in the middle of the stream, the current may be more manageable on either side, making it a good place to cross.”
That may or may not be true for the speed on a roadway, but at least a pedestrian refuge island reduces the width that needs to be crossed and makes the pedestrians more obvious to the drivers. If you put vertical elements in the island (without blocking the view of the pedestrians), it absolutely will slow the flow.
“Cross at a straight section. Imagine the bends of a river forming the letter "S" - the safest place to cross is generally the straight section in the middle of the "S" between the bends.”
A crossing at mid-block is like crossing a river in a straight section. Marked mid-block crossings have fewer conflicts for drivers to navigate. As drivers approach the crossing, they’re looking straight at the person crossing and they’re not trying to watch out for another vehicle that could come hit them. Note: In suburban areas with large parking lots, it makes a lot of sense to line the crossings up with the setbacks for the buildings. Pedestrians don’t really want to cross that parking lot to get themselves to the intersection in the ROW anyway. They want to be close to the front of the building where the doors are and they’re going to want to cross where the buildings line up.
“Glacial streams are often easiest to cross in the cool, early mornings when the volume of water is lower making them shallower with a slower current. Current can rise significantly within a few hours on warm sunny days or after heavy rains, making a slow stream an impassable torrent.”
Downstream of a signal, what is genuinely safe off-peak may be really dangerous during peak hours. Upstream, the opposite holds. Pedestrians often get used to crossing during off-peak hours and then try to risk it at a busier time of day. Designers need to be aware of the demand and give crossings where they are needed.
Parking lots:
One other metaphor seems to be valuable: for a pedestrian, crossing a parking lot (especially in the Florida sun) is akin to crossing the dead marshes. Even Gollum knows, “Not a pleasant place, my precious.”
Building out the metaphor on the ground
There is still much to do to determine how much demand is too much or how much flow is too much and how those amounts mix with the crossing width. Marked mid-block crossings with overhead signals are very expensive. As we begin to have more pedestrians and cyclists in our system, we’re going to need them. Figuring out less expensive ways to make these crossings work would probably make someone a mint.
One thing I did notice when we evaluated complete streets before and after the “improvement” was that any time cyclists ended up crossing flows, crashes were unavoidable, no matter what type of treatment you gave them. Slip lanes do reduce right hook crashes, but then you have cyclists sandwiched between two different travel streams—and it’s easy to get swept away when you’re in that current. You’re trading one type of crash for an even faster speed risk and a deadly sideswipe. The data I saw absolutely convinced me the only successful strategy will be to move to two stage left turns and protected intersections. Remember, if it’s not safe for a 7 year old, it’s not really that safe (After seeing some amazing successes lately, I may revise that to a 4 year old…) A recent study that was highlighted in Streetsblog went even further. Protected bike lanes increased cyclist safety. On-street lanes had no impact. Sharrows made things worse.
Up next:
Next week I’m speaking at the International WTS Convention in New Orleans. I’m going to try to post pictures of cool things—and New Orleans always has cool things to see from a street standpoint.
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