Tag: posted speed

SacCity design speed

Dan AllisonLeave a comment

Note: A reader asked how a driver would know whether they are on a street where the design speed is well above the posted speed, or whether they were on a street where the design speed was equal to the posted speed. That is a reasonable question. A safely designed street communicates through design what the intended speed is. However, our traffic engineering profession has trained drivers very well with the expectation that it is safe to exceed the posted speed. There will be a transition period as drivers learn 1) to pay attention to the street and what it signals, not just what the sign says, and 2) that new and reconstructed streets are designed for safety of all users, and therefore the design speed equals the posted speed. But in the meanwhile, drivers will need to know. So, I’ve added a sign below that could be used to signal design = posted, with a red border. The color of the sign itself can’t be changed because in our sign system (MUTCD), white is regulatory.

Part of an ongoing series of posts to support better streets in the City of Sacramento during their 2023 update of Street Design Standards. New standards must be innovative, safe, and equitable, and it will take strong citizen involvement and advocacy to make them so.

Streets are designed for a specific speed limit, which is almost always well above the posted speed limit. The original theory was that designing for higher speeds would protect drivers who drive over the posted speed limit. This is outmoded thinking, for two reasons. One is risk compensation, that most drivers will drive at a speed that feels slightly unsafe, so they are driving just over the design speed. Two is that even if the design speed is safe for drivers, it is not safe for walkers and bicyclists.

The points below are policy, not specifically designs. I have realized that it is not just the design standards that need to be updated, but the policies that determine what design will be used in various context. A lot of city policies are not documented, but reside in the minds of the planners and engineers. Because they are not documented, the public can’t evaluate them and ask for changes.

  • Design speed = posted speed; a street will never be designed or reconstructed for a higher design speed than the posted speed limit
  • Design and posted speed limits will be set at a level that ensures safety for all street users including walkers along and crossing the street, and bicyclists
  • All projects that reconstruct or reallocate a street must consider a reduction in the design and posted speed
  • Lane widths must match design speeds; lane widths will be limited to 9 or 10 feet except that one lane on truck routes, bus routes with 15 minute or better frequency, or dedicated bus lanes may be 11 feet
  • Local streets will have a design and posted speed of no more than 20 mph
  • Streets intended for both local and through traffic may have a design and posted speed of up to 30 mph
  • Streets will not be designed or posted for 40 mph unless the design reduces intersections, and reduces or eliminates driveways and turning movements
  • No street in an urbanized area will be designed or posted over 40 mph

Choosing streets to bike

Dan AllisonLeave a comment

20130817-131452.jpg
M Street bike route
As I said yesterday, I choose primarily two-way, two-lane streets to walk on, because they offer a quieter and calmer place to enjoy walking, looking around, and finding businesses to frequent. When bicycling, I’m more likely to be going someplace specific, and more likely to be in more of a hurry. If given the time, I’d almost always rather walk than bike, but bicycling certainly saves a lot of time, and so I bicycle more than walk.

The first criteria for choosing streets to bike on is traffic speed. In the grid, nearly all of the streets are posted 25 mph, but traffic speeds vary widely from 20 to 40 mph. When a street is designed for 40 and then posted for 25, motor vehicle drivers respond by going 40. Again, this is a street design issue. I am not afraid of 40 mph traffic, and I am OK mixing in with it – I’m a vehicular bicyclist, but why, when I don’t need to? So I pick other streets.

First preference is quiet streets with a design or signing welcoming to bicyclists. Best example is M Street in East Sacramento, my usual route to and from Trader Joes, and also when I jump off the parkway at Sac State and continue into downtown/midtown. Streets like M are the closest Sacramento has to bike boulevards or neighborhood greenways.

Second preference is narrow streets without bike lanes. Why? Because the traffic moves slowly on these streets, sometimes below the posted speed. Since I’m now treating stop signs as yield signs, the more frequent stop signs on these streets don’t slow me down very much, there are few vehicles to take turns with except at two brief times of day. Parking along these streets helps a lot, particularly when it is diagonal, because parked cars create friction that slows drivers.

Third preference is streets with bike lanes. But often these are higher volume, higher speed streets. If I’m really in a hurry, these are the streets I use. Fewer stop signs and fewer signals make for a faster trip. In that sense I’m making the same decision as car drivers.