Tag: traffic calming

Hmm. 16th St traffic calming

Dan Allison2 Comments

A new traffic calming feature has showed up on 16th Street approaching R Street in midtown Sacramento. Paint and flex posts have been placed between the travel lanes. Advance yield lines (‘sharks teeth’) were also painted, showing where drivers should stop when yielding to pedestrians.

16th St lane channelization

I’m not sure what to think of this. Certainly this is a problematic intersection. Cars stopped for the light rail gates between R Street and Q Street often stop throughout the intersection, blocking both the north and south crosswalks over 16th Street, as well as the intersection itself, preventing vehicles along R Street from proceeding while the traffic is stopped. As with all multilane streets, but particularly high speed, one-way arterials, drivers in one lane may stop for a walker while the others will not. I see this every day, and this intersection is worse than most. For reasons I don’t understand, traffic speeds on 16th Street northbound are noticeably higher than 15th Street southbound, even though the design of both streets in the same.

So, how’s it working. Well, I’ve so far only had the chance to observe it for 15 minutes. I’m not sure it is making much difference. About 10% of drivers stopped at or close to the advance yield lines. About 70% of drivers stopped at the forward edge of the flex posts, about 10% stopped over the crosswalk, and about 10% did not stop for people using the crosswalk. I saw three people nearly hit by drivers. This is not unusual, and it not worse than before, but it is not good.

Below is an example. The driver to the left stopped over the top of the crosswalk, even though it was clear that traffic ahead was stopped for the light rail gate, and there was no space to proceed into. The driver to the right stopped before the crosswalk, but not at the advance yield line. Not visible it the driver in the closest lane who did not stop at all because there was a space in that lane across the intersection.

walker using the crosswalk over 16th St at R St

While I appreciate the effort, I’m not sure if the results will be what is desired, which is the ability of walkers to safely cross the street.

In the long run, the reallocation of roadway on 16th Street to reduce the general purpose lanes from three to two will help this location a great deal, but I don’t know when that will happen. It could be years away.

With the new businesses on R Street to the east, and the street dining area on R Street to the west of 15th Street, this intersection has become quite busy with walkers, bicyclists, scooters, and motor vehicles. It does deserve attention.

traffic calming in the central city

Dan Allison1 Comment

There are four types of traffic calming that have been used in Sacramento central city: median islands, traffic circles, traffic diverters, and speed humps. It was recently said by city staff that only speed humps are a current solution for traffic calming, but I’d really like the city to bring back diverters.

Median islands: These islands, placed at the approaches to intersections, provide some traffic calming effect, offer walkers a refuge in the middle of a crossing (though it does not meet current ADA standards for refuge). Below is a typical setting, this one at D Street & 23rd Street. Though the median does slow some drivers, other drivers use these as slalom courses. On streets with bike lanes, the bike lanes are generally dropped before the intersection in order to accommodate the median, but his is poor practice, leaving bicyclists either feeling vulnerable or actually vulnerable at just the wrong location.

median island, D St & 23rd St, Sacramento

Traffic circles: Traffic circles deflect drivers to the side, a somewhat more effective solution, but have the same problem for bicyclists as the median islands, with bike lanes dropped at the critical point. These traffic circles are NOT roundabouts. A correctly designed roundabout allow the bicyclist to choose between continuing in the general purpose travel lane, or using a sidewalk or sidewalk adjacent bypass. Roundabouts also have a continuous flow, only requiring a driver or bicyclists to yield to someone already in the roundabout, but traffic circles have stop signs on one of the cross streets. Roundabouts also have enough deflection that a driver must slow down to navigate, whereas most traffic circles have only a slight deflection and therefore limited slowing value.

The central city does not have any roundabouts, and they are rare in the region. They can be a reasonable solution at the intersection of two arterial roadways, again, IF correctly designed. The footprint of a real roundabout is bigger than an urban intersection. Below is a typical setting, this one at 13th Street & F Street.

traffic circle, 13th St & F St, Sacramento

Speed humps: Speed humps slow drivers crossing over them. Many people still call these speed bumps, but the sharp bumps are now illegal on streets and are only found in private parking lots. These can also be speed tables, longer than the humps, perhaps higher, and sometimes hosting a crosswalk on top. There are two problems with humps: 1) drivers with good suspensions can sail over these without slowing, and ironically the drivers of high value motor vehicles are the ones most likely to have good suspensions and to not slow for any reason; and 2) drivers accelerate back to speed immediately after the hump, so it only has a traffic calming effect at that particular point. Often speed humps have cut-throughs for emergency vehicles, so they don’t have to slow, but wide stance pickup trucks can use the same cut-throughs, and the cut-throughs are often placed so as to inconvenience bicyclists.

Stop signs: Stop signs calm traffic somewhat by requiring drivers to slow at intersections. Anyone who thinks that drivers actually stop at stop signs, in the absence of conflicting and risky traffic, has not actually stood at an intersection and observed driver behavior. Almost no one stops at stop signs unless they have to. This includes law enforcement officers. Stop signs are the most commonly requested traffic calming solutions by people who live on or near the street. But they are simply not very effective. Drivers accelerate away from the stop signs and are soon going just as fast as they were before, likely 10 to 25 mph over the posted speed limit. While not a major issue, this stop and go traffic adds to air pollution.

Traffic diverters: Traffic diverters turn motor vehicles off a street, but allow bicyclists through. There are a number of these in the central city, and in my opinion, they work great. The subsequent blocks are quiet and safe, at least until the street has regained traffic from other directions. They make is difficult to continue for long distances in a single line of travel, which is a good effect, as it discourages low value driving trips. My observation is that these also increase compliance with stop signs. It is true that some scofflaw drivers will go around these diverters, but at least they have slowed considerably to do so. Below is a typical diverter, this one at 20th Street & D Street.

traffic diverter, 20th St & D St, Sacramento

There are a number of other traffic calming treatments, but so far as I know none are present in the centra city, so I’ve not addressed them.

I don’t think the city should install any more median islands or traffic circles, due to the negative impact on bicyclists. However, I’m OK with letting those that exist remain, as bicyclists and walkers have grown accustomed to them and mostly know how to deal with them. I’m against more stop signs, except where a stop-controlled intersection replaces a signal-controlled intersection (of which there are a number of candidates in the central city). I don’t think speed humps are effective, and I see a speed hump as an admission of a failed street design.

What I would like to see is more traffic diverters, many of them! Every street that is not a one-way arterial in the central city should have a diverter about every eight blocks. This will make is less pleasant for commuters, who have to zig-zag to get where they are going. It will also cause locals to reconsider driving trips, realizing that bicycle or walking trips are easier and more straightforward. It will ensure that more of our streets are calm and peaceful, with less driver intimidation of walkers and bicyclists.

I hope to find the time to make a map of all the traffic diverters in the central city, and will add that reference here when I do.

prudent drivers as traffic calming

Dan AllisonLeave a comment

Now, on to why I brought up the topic of prudent drivers. A prudent driver on a two lane (one lane in each direction) roadway largely controls the behavior of irresponsible drivers. On wider roads, with two lanes or more in a direction, whether a one-way or two-way, the irresponsible driver can do as they wish, violating laws and endangering others. On the narrower roadway, the irresponsible drivers get irritated, and honk and cuss, but there isn’t much they can do about it. This difference in large part explains why fatality and severe injury crashes are rare on residential streets within neighborhoods, and are common on arterial streets with multiple lanes. It also explains why rural roads have such high crash rates, because the prudent driver there can’t really control other drivers. On two lane streets, prudent drivers set the tone; on multiple lane streets, irresponsible drivers set the tone.

We have proven, over the history of motor vehicle use in the US, that is is not possible to significantly change the behavior of drivers. Education doesn’t do it, enforcement (even when that used to be more common) doesn’t do it. Nearly all of the improvement in roadway deaths has been due to safer cars, not to safer drivers or safer roads, and now that improvement is reversing itself as more and more walkers and bicyclists are killed by irresponsible drivers.

I am not against education, if it is directed at the most dangerous behaviors, which it is not, and I am not against enforcement, if it is done in an unbiased manner, which it is not. Each state has an agency, usually called the Office of Traffic Safety (OTS), whose mission is to obscure the real causes of crashes and to blame walkers and bicyclist for their death and injury, and at the federal level, the National Highway Traffic Safety Administration (NHTSA) fulfills this function admirably. In this, they are often aided and abetted by the law enforcement agencies. The reason CHP is California is so opposed to automatic speed enforcement is because it would remove the mis-focus and bias that they otherwise rely upon.

Driver behavior must be controlled by roadway design. That is why I strongly believe that all multiple lane roads must be reduced. Two lane one-way streets must be converted to two-ways streets with only one lane in each direction (and any other lanes converted to pedestrian, bicyclist or transit use). Two-way roadways with two or more lanes in the same direction must be reallocated to other uses. Again, excess capacity would be converted to pedestrian, bicyclist, or transit use, or even to development as overly wide streets shrink to fit the real need.

I have no illusions about the huge change in traffic flow. Those drivers who have gotten used to having plenty of space for themselves (their cars) would have to figure out how to use less: fewer trips, shorter trips, slower trips. People would make different decisions about where they live, where they work, where they shop and recreate. As far as I am concerned, this is all to the good.

Our freeways are designed by the ‘best and brightest’ engineers to be as safe as possible, allowing errant vehicles extra space, protecting hard objects with guard rails and impact attenuators (crash barriers), and using ridiculously wide travel lanes, yet still have very high crash rates. Spending more money apparently doesn’t make freeways safer, and the explanation for this is risk compensation, the proven effect that irresponsible drivers will increase their unsafe behavior to maintain the same level of risk. Think about the daily news items about crashes that close freeways for significant periods of time, and how often they happen. None of these need to happen, and I’d argue that an irresponsible drivers is the primary cause of each and every one of them. This post is about local streets, not freeways, but it is worth remembering that irresponsible drivers are everywhere.

I don’t believe that one single death or severe injury for a walker or bicyclist is worth any amount of convenience for motor vehicle drivers. Not one.

So, I ask every transportation agency in the Sacramento region to:

  • cease widening roads, forever
  • analyze all one-way roads with three or more lanes to determine the most dangerous ones, and convert these within two years
  • analyze all two-way streets with more than one lane per direction for the most dangerous ones, and convert these within five years
  • analyze the remaining roads that are not one lane per direction, for the most dangerous ones, and convert these within ten years
  • complete conversion of all roads within twenty years
  • stop victim blaming

I & 12th crashes

Dan AllisonLeave a comment

The city has installed substantial bollards on the southwest corner of I Street and 12th Street in an effort to protect the Bangkok@12 Thai Restaurant there.

There were at least two major injury crashes into the restaurant in 2019, and the location has a history of crashes (see https://www.sacbee.com/article235349392.html for one example). There were 26 collisions at this intersection in the five year period 2015-2019. This is the most for any intersection in the central city, with the next closest being 19th Street and X Street, at 17.

2019-09-20 crash (photo from SacBee)

Why? Well, the primary reason is that this is the intersection of two 3-lane, one-way arterials, both of which are known to have a history of speeding. The city installed a speed display sign on 12th Street approaching I Street, but has not done so for I Street approaching 12th Street. I had not noticed this sign before yesterday, so I don’t know how long it has been there. Even a brief watch of it indicated that many drivers are exceeding the speed limit, some egregiously so, at more than 10 mph over the speed limit. And then, of course, there are the bollards pictured above. These are not solutions.

The city has identified the section of I Street east of 12th for a reduction in travel lanes from three to two, and that will help. But to the west, no reduction, so drivers will likely be speeding up through the intersection to spread out into the increased capacity. For 12th Street, a reduction from four (!) to three lanes will occur north of H Street, which may reduce speeds approaching here, but in the section between H Street and J Street, it will remain three lanes.

I strongly feel that all roadways of three or more lanes must be reduced to two lanes. Drivers simply cannot be trusted to behave properly on 3-lane roads. It doesn’t matter how much signing we add, or bollards we add, drivers will still speed and will endanger walkers, pedestrians, people in other vehicles, and people sitting down to eat a meal at restaurants.

Solution? The reduction in lanes on I Street must continue westward at least to 10th Street (I would continue it all the way to the freeway, but that is another issue). 12th Street must be reduced from three lanes to two lanes in the section between H Street and J Street (I would reduce it from C Street south). Most of the traffic on 12th Street turns left onto J Street, only a portion continuing south, so having one through lane and one left turn lane would not significantly reduce capacity, but would make things a great deal safer. A bonus would be that the left hand travel lane can be allocated to the exclusive use of the southbound light rail tracks. Currently, the southbound lane is shared between motor vehicles and light rail, and the light rail train is often delayed by congestion and by left turning vehicles. Two birds with one stone, as the saying goes.

The city’s Vision Zero effort focuses on corridors, stretches of street with a high crash rate, and this is not a bad focus, given that most of these corridors are in disadvantaged/disinvested communities. It does not focus on intersections, not even on very high crash rate intersections. San Francisco’s Vision Zero program, one of the leading in the country, identifies the top five corridors, AND the top five intersections. There has been significant though not necessarily complete infrastructure work on each of these. I would like to see the I Street and 12th Street intersection be prioritized for Sacramento.

Roundabouts and traffic circles

Dan Allison7 Comments

It is common for people to use the terms roundabout and traffic circle interchangeably, as though there is no difference between the two. Sadly, Streetsblog San Francisco, whose mission is to educate the public, claims that there is no significant difference and that it is OK to use the terms interchangeably (SFMTA Launches “Muni Backwards” Program). That is not true.

A roundabout has two very significant features:

  1. significant horizontal deflection which slows traffic
  2. yield signs at all approaches

Traffic circles do not usually have these features.

Sac_7th-St_roundabout
roundabout, Sacramento

The photo at right shows a roundabout in the River District/Township 9 in Sacramento. It is quite a bit bigger than a roundabout needs to be, and was installed in a new development, not at an existing intersection, but you can see the deflection and yield signs.

Significant horizontal deflection means that vehicles must change significantly from a straight line of travel, which requires that they slow significantly. This slowing reduces the number of crashes somewhat, and almost eliminates the number of severe crashes and fatalities (about 80% reduction). They are safer because they greatly reduce the number of conflict points in an intersection.

R6-5_288Yield signs on all approaches means that vehicles only have to stop for other vehicles already in the roundabout. Otherwise, they proceed at their reduced speed and never have to stop. This yield approach benefits motor vehicles and bicyclists who ride in the travel lane. It does not, and is not really intended to, benefit bicyclists in bike lanes or pedestrians, but at the same time, if does not hurt them. There is one standard MUTCD sign used at roundabouts, shown at right, but you will also see many other signs at both roundabouts and traffic circles.

traffic circle, Sacramento

Traffic circles vary widely in size, and therefore the amount of deflection. At least in California, they almost always have stop signs on two of the approaches, so that one street does not stop and the other does. The photo at right shows a traffic circle in downtown Sacramento. It has some deflection, but not enough to really slow traffic, and with the stop sign, does not ease the flow of traffic. These traffic circles also squeeze bicyclists who do not know they need to take the lane to safety navigate the intersection. The traffic circle sign is not a federal or state standard sign, but does communicate.

There are a a number of traffic circles in Sacramento central city, most of which were put in years ago, but a few newer ones also exist. Depending on the size of the circle, they have varying traffic calming benefits. The reason traffic circles are used instead of roundabouts is that you can’t just plop a roundabout into the footprint of an existing urban intersection. They require more space.

There are a lot more features of roundabouts than just the two that I mentioned. If you want to become a traffic nerd on roundabouts, I recommend the FHWA roundabout page, particularly the publication Roundabouts: An Informational Guide, Second Edition. For an international best practices perspective that focuses on bicyclist benefits, check Explaining the Dutch roundabout abroad.

Multi-lane roundabouts probably do not have significant safety outcomes over regular intersections. Many Sacramento people have experienced multi-lane roundabouts in Roseville and in Truckee at the Interstate 80 – Hwy 89 interchange. It makes me nervous to even watch these, and I always label these as multi-lane roundabouts to distinguish them from single-lane roundabouts or just roundabouts, which do have very significant safety outcomes.

SF_new-traffic-circle-McAllister-LyonLastly, the type of traffic circle that engendered the discussion in San Francisco is at right. It has several non-standard features, even given the variability of traffic circles.

Choosing streets to walk

Dan Allison2 Comments

business on a two-way, two-lane street (Capitol at 18th)
business on a two-way, two-lane street (Capitol at 18th)

I walk a lot in midtown, going to and from various destinations such as the train station, nonprofits and agencies I work with, grocery stores, theatres, farmers markets, breweries, etc. I was thinking last night as I walked to and from Capital Stage about what streets I choose to walk on.

Almost all the time I choose to walk on two-way, two-lane streets. I rarely choose to walk on the multi-lane streets and the one-way streets, except for short distances as I zigzag to my destination. The two-way, two-lane streets are usually quieter, less traffic and traffic moving more slowly. I can relax more with the quiet, and I can look around more, paying more attention to everything around me and not just traffic.

Why is this significant?

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doubting protected bikeways

Dan Allison1 Comment

Protected bikeways, also called separated bike lanes or cycle tracks, are all the rage these days. The NACTO Urban Bikeway Design Guide codified cycle tracks, but they were already showing up in several cities, and are now being implementing in a great number more. I’ve ridden on cycle tracks in Long Beach, San Francisco (just yesterday, in fact) and other cities, and yes, they are a pleasure to ride on compared to riding in traffic or traditional bike lanes. Many people have declared the era of vehicular cycling dead, and the era of protected bikeways upon us.

So why am I doubting?

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What are stop signs for?

Dan Allison1 Comment

Rosswood-GrandOaks_crosswalksIn the month of May I bike commuted to work in Carmichael and Citrus Heights most of the days. I had plenty of time to think about stop signs, as there are a lot of them on my regular routes. A few less, now that the county has removed some from the parkway path, but still, a lot. At most of these stop signs, there are no cars anywhere in sight, particularly at the beginning of AM and PM commute hours when I’m riding, but even at other times of day. So I started thinking, why are these stop signs here, and what are stop signs for?

Stop signs get used for these purposes:

  1. When there is a busy intersection with a more or less equal flow of vehicles on both streets. The four-way stop signs assist people in taking turns.
  2. When one street is so busy that gaps long enough to cross that street are rare.
  3. When there are visibility issues that prevent vehicle drivers to see each other.
  4. When motor vehicles are going too fast, and they need to be slowed down.

Looking at each purpose in more detail:

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What is a roundabout?

Dan Allison1 Comment

I have noticed a lot of confusion in Sacramento amongst both transportation professionals and citizens interested in traffic calming about roundabouts. If you live, work or play in downtown and midtown Sacramento, you’ve seen a lot of structures in the intersections which people call roundabouts, but which are not, they are traffic circles. So what is a roundabout?

intersection conflict points
intersection conflict points

A modern roundabout is a structure that allows a free flow of traffic without stop signs. Instead, they use yield signs and markings. They are most appropriately used at street intersections where both streets are fairly busy. The biggest advantage of a roundabout, for all users, is the reduction of conflict points in the intersection from thirty-two to four, as illustrated in the diagram at right!

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