Comments
dumnezero t1_ixh2tmm wrote
Rules without enforcement are just recommendations
defcon_penguin t1_ix7pvud wrote
20 mph for residential areas and side streets, make perfect sense. For main roads where most traffic is, makes no sense
MondayToFriday t1_ix9j8ir wrote
Motorists tend to drive at a speed they feel comfortable with, rather than at the posted speed limit. If the speed limit is lowered without alterations to the road design (narrowing the roadway, adding roundabouts, etc.), then it makes sense that lowering the speed limit has little effect on safety.
SlightlyScruffy t1_ix7k9yk wrote
The scheme did slightly reduce vehicular traffic, and very slightly reduced speeds, which between them must have had an effect on air quality too.
Competitive_Ninja839 t1_ix84n8a wrote
Could the reduced vehicular activity just be drivers choosing other roads with higher speed limits?
_DeanRiding OP t1_ix88lvx wrote
Possibly. I know Google Maps definitely tries to avoid 20mph roads on my route home from work despite those roads having less traffic and actually being quicker.
Competitive_Ninja839 t1_ix89ao1 wrote
That's Google maps for you. Meanwhile where I live, it recommends one of the most dangerous highways in America over a safe state route because it shaves 3-4 minutes off an hour commute.
seamustheseagull t1_ix7xl9k wrote
Casualities too. The conclusion mentions no significant change in casualties, however the data suggests otherwise, especially for pedestrians.
The low sample size means it's far from definitive, but certainly enough of a differential to warrant consideration.
A reduction in traffic volumes + a potential/likely decrease in pedestrian casualities suggests that this is a good intervention to consider for city centres.
[deleted] t1_ix80nf2 wrote
The data does not suggest otherwise. As you pointed out the sample size is way too low to draw any reasonable conclusion. So i don't know why in your next sentence you completely ignore that and continue on as if it does.
If an intersection only has 3 incidents per year on average and then after the study there are 2 incidents, it doesn't mean we can conclude that there was a reduction because of the speed limit.
seamustheseagull t1_ix87oe4 wrote
No, but it may warrant further consideration. Certainly not conclusive enough to say, "no change was noted".
It's a common false-negative problem. "The differences were statistically insignificant" is only valid when you have a reasonable sample size. While technically it is correct to say, it implies a conclusion where none can be drawn.
[deleted] t1_ix92xnk wrote
>it implies a conclusion where none can be drawn.
No effect is literally a conclusion that can be drawn.
fatsynatsy t1_ixbw3n2 wrote
inappropriately drawn... as the sample size is too small to find a small effect with statiscal significance.
[deleted] t1_ixcpk6h wrote
Because the amount of accidents in the first place is small. So reducing speed limit isint going to have an effect since the effect was so small in the first place.
fatsynatsy t1_ixgrdio wrote
I see your point, but I would argue that no effect is still different from an effect which is functionally insignificant or outweighed by the inconvenience associated with a reduced speed limit.
[deleted] t1_ix8aicv wrote
Would that effect air quality much? Vehicles moving slower means they're releasing emissions in the area for longer.
AllanfromWales1 t1_ix7jp2u wrote
We have such a scheme in the town I live in, and as the paper says it has made minimal difference to speeds or to accident rates. However, I suspect three years is too short a time to draw definitive conclusions. Many people who drive around town just do what they always did without consideration of speed limits. There is (anecdotal) evidence, though, that newcomers to the area and/or new drivers are driving more slowly, and as their numbers increase over the years things may get better.
gizahnl t1_ix7sa52 wrote
This is the reason why we in the Netherlands when lowering speed limits also change the design of the street, to make it more uncomfortable to drive fast. I.e. roads are made less wide, trees are planted closer to the road and in greater numbers etc. This is (supposedly) more effective than speedbumps.
AllanfromWales1 t1_ix7sgex wrote
Certainly more effective in lowering speeds, but not necessarily less dangerous. Trees closer to the roads, for instance, mean less time to see if a child runs out into the road.
gizahnl t1_ix7v3zh wrote
Not that close ;) It's more to give a much stronger sense of motion when you're driving and trees are swoosh-swooshing past. It makes you feel you go fast, while without you'd speed up.
Streets where kids are likely to pop up on the street usually are woon-erf. Speeds limited to 15kph, ped priority /everywhere/ (i.e. allowed to walk & play anywhere on the street) and a different layout that further inhibits speeding.
[deleted] t1_ix9jces wrote
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_DeanRiding OP t1_ix7k07b wrote
I've personally found that if road conditions are permitting, people often (sometimes dangerously) overtake those doing the 20mph limit as well which I could actually see increasing accidents (anecdotally such an incident occurred just outside my house).
AllanfromWales1 t1_ix7ly8t wrote
Not seen overtaking here (the roads aren't well suited to that) but tailgating is commonplace. That's even true in 30mph zones with someone driving at the limit.
agate_ t1_ix9e74z wrote
Traffic ticket revenues were way up, though, so lawmakers say it’s a win.
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rkhbusa t1_ix7jx32 wrote
20MPH that’s a deaf children playing speed limit, I’d be so pissed if my city centre dropped the speed limit to 20MPH.
oreygkira t1_ix7m5bf wrote
Exactly, we should ban cars from city centers altogether.
xopranaut t1_ix7mvut wrote
If you look at table 3, it’s clear that actual speeds in the monitored areas were very rarely much above 20mph before the new limits were introduced, which makes the rest of the observations moot.