Sunday, 24 April 2016

Stroad

If you read the title, you might think I have bad spelling. But as you'll see, I am never late nor early, I mean precisely what I mean to (Hobbit jokes). I was inspired to write this because Edmonton released a spinoff guideline around "Main Streets", link here: http://www.edmonton.ca/city_government/documents/MainStreet_Guidelines_Feb2016.pdf

A stroad is a portmanteau, combining the words road and street. The main characteristics are that it has some sort of local access function while also trying to be a place where motor traffic is trying to get from A to B. Japser Ave in Edmonton is an example, as is Whyte Ave. To a lesser extent, this applies to arterial roads which have parking lot accesses directly off of them. Usually it's used in the context of trying to be a place where pedestrians are expected.

Many of these have very bad safety records. I will explain why shortly. To try and address this safety record and the image as being a place for cars, many cities are trying to make them "complete streets", I explained why this will fail as well if we try to follow Edmonton's guidelines on this or similar documents, by adding protected bike lanes, widen the sidewalks, add a bus lane or two and add plants. It is unlikely that these are going to make much of a difference. A lot of roads in NYC have protected bike lanes and bus lanes but still the streets are congested and full of cars with bad safety records.

So why are they so dangerous? If we look at Sustainable Safety, they violate three main principles: functionality, homogeneity and predictability. It may or may not be forgiving of error as well depending on the specific design. In Sustainable Safety, a thoroughfare is safe if it is either for local access, or for getting from A to B, but not both at the same time. It should be for exchange or flow on a link, but not both. Based on the way that these stroads function, they'd be distributor roads, because they are intended to be the main ways that people get from their local streets to the highways and motorways, but they are otherwise very bad distributor roads. They focus on exchange on the links but it also focuses on flow on the links.

It violates the homogeneity principles as well. It combines many different speeds, masses and directions into one place. This is exasperated when you don't have separate cycle paths. The trucks on these roads are large, often over 12 tonnes, but they have to mix with ~1 tonne cars and small bicycles and pedestrians. A bus is the only thing that is likely to be comparable. Buses have the same problem. One tonne cars often mix with cyclists in the traffic lanes. Cars often park on the side of many stroads, so hitting them is a conflict. Because of the large number of minor side roads, a lot of traffic has to make turns. Each minor 4 way intersection is an additional 32 conflict points. And this is just assuming that there aren't multiple lanes for motor vehicles in each direction, no pedestrian movements, no bicycle movements, no bus lanes, just a simple 2 lane road crossroad. Many of these are crossing conflicts. The speed of traffic is often just slow enough to be inefficient for getting anywhere but just fast enough to make the conflicts dangerous. At speeds over 30 km/h, a crash between a moped, bicycle or pedestrian and a car or truck or bus is going to be much more dangerous. 90% survive at speeds of 30 km/h or less but less than 50% at 50 km/h, and at 30, you have more time to react.

And it violates the predictability element by combining the functions of an access road with the functions of a distributor road. The multiple lanes paved in asphalt sometimes with a median with traffic lights and priority over side roads makes it feel like a distributor road for medium speed traffic at medium volumes, but the buildings, parking, local access and pedestrians makes it feel like an access road. You don't know what is expected of you. Especially given that many stroads tend to try to lower the speed limit from perhaps 50-60 km/h to 30-40 (30-35 down to 20-25 mph), but the physical design doesn't change much. You have little time to react when you make a right turn, you often have to shoot for the gaps when making a left turn if there is oncoming traffic. You have less ability to gauge how to behave here. And this is under ideal conditions. Let alone the night, fog, thick snow, etc.

The best solution is to downgrade the roads to a 30 km/h zone. Divert as much of the traffic as you can, and if the volume is sufficiently low and the big heavy traffic is gone or is restricted (no buses if possible, and vans or other trucks under 3500 kg deliver goods at certain times of the day when there is less traffic, then begin to mix cyclists and motor vehicles. This should never be a shared space as Exhibition Rd in London or the Kerkplein in Assen works where there is too much traffic for mixing to work, but a low volume street is what we want. Banning cars altogether is another option.

If you cannot downgrade to a 30 km/h street, then remove as many conflicts of the distributor road as possible. Remove as much car parking as you can, close off minor side roads to motor traffic or if they really need to exist, make them right in right outs. Ban left turns from the distributor road at arterial to arterial road junctions too. Add simultaneous green and or the protected junction, preferably with separate signal phases. Make it be so that only a single lane for motor vehicles in each direction remains, and separate the traffic with a median. Add cycle paths that are well protected and wide, and also continuous. Make any side street crossings open to motor traffic into a gateway design with a continuous sidewalk and cycle path at the same level and make the cars go up and down curbs. Restrict deliveries, put bus stops in separate bays if they do not have physically separated bus lanes. Restrict the corridors that the buses use, so that they pose less of a danger on as many corridors as possible. Make minor side road crossings where pedestrians and cyclists still cross into safer crossings with the motor traffic going at a speed of 30 km/h by making them go around a median with tight curves and a raised table with an advisory speed of 30 km/h and a zebra crossing with a median refuge for cyclists too to wait in the middle. Remove objects from the clear zone, on a 50 km/h road I believe that this would be 1.5-2 metres when possible from the right edge of the curbside lane. Remove objects from the sightline triangles.

Stroads should never be intended by design, and existing ones need MAJOR modifications to avoid being the deathtraps for pedestrians and cyclists and congestion wells they are today. They are inefficient, dangerous and not helping anyone.


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