Laura rants about traffic lights

[firstfrost]

So, these signals have been bothering me for a while. The first one, I finally partially figured out, but I still think it's inefficient. The second one, is just WRONG.

Anyway. This is the intersection of the one-way Dover Street with Mass Ave, in Cambridge. At the intersection, Dover is two lanes - one left turn lane, one right turn lane.

When it's time for Dover Street to go, you get a green right arrow only first, and then a green left arrow only. At neither time does any other lane have a green light. The only reason for this somewhat perverse splitting up of the leftgoers and the rightgoers is that the crosswalk is on the right, and they get a walk light during the left-only light. But there's no reason that the leftgoers couldn't be going while the rightgoers are already going. There's no crosswalk on the left, and none of the cross traffic is going. Also, I think this is more concern for the people in the crosswalk than Mass Ave shows anywhere else - pretty much everywhere else, it's perfectly happy to have the walk light on a straight-plus-turning-included green. And the crosswalk two down has no lights at all, it's just "cross when it doesn't look like anyone is going to kill you." Not that I object to doing something nice for the pedestrians, but it surprises me because it's so unusual. I do object to being inefficient with the leftgoers, though. :)

The other Intersection of Inexplicability is four blocks down, at Cameron and Mass Ave. Let me describe the intersection. Mass Ave is two lanes on either side of the divider. Cameron Ave, to the right, is one of the more major smaller roads - it's a snow emergency route, it's the first through street past the bike path, it has a lot of traffic. To the left is Harvey Street, which is tiny and one way away from Mass Ave. I used to say that I never saw anyone turn left onto Harvey Street, but while I was hanging around taking pictures, I did finally see one person do so.

Anyway. When the light turns green on Mass Ave, the northbound folks briefly get this set of lights before the full green:

I can kind of see the point in giving someone the chance to take the left before the oncoming traffic gets to go, in case there's a lot of traffic. But why give the left to Harvey Street, rather than to the people going south who might want to turn left onto the much more travelled Cameron? But that's not even the real question. The real question is, why on earth is there a left arrow from the right lane? You can have two lanes of left turning people when you have a lot of people wanting to turn left and the leftmost lane is a dedicated left-turn-only lane. (Like going from Mass Ave left onto Somerville Ave, in Porter Square - there's a left turn lane and then a left-and-straight lane and then a straight lane. But it makes no sense at all here. The left lane isn't left turn only. Almost nobody turns left. Harvey street has only one lane, it doesn't have room for two lanes worth of left turners at once. Turning left from the right lane would be the worst idea ever. So.... what the heck?

Comments

[kirisutogomen.livejournal.com]

How about, both lights are always the same and apply to both lanes? Generally we AND our traffic instructions together; I'm in the right lanes, so I'm allowed to {turn right, go straight, stop} and the traffic light has green plus a green left arrow, so I'm allowed to {turn right, go straight, turn left} and the intersection of those two sets tells me what I'm actually allowed to do.

Having both lights always the same means that if for whatever reason one light isn't visible -- maybe a bulb burned out, maybe part of a vehicle is obscuring it, maybe a giraffe on a scavenger hunt stole it -- people still get the signal information.

[firstfrost.livejournal.com]

Okay, I can accept that as a definition that makes sense, but I do not think that this definition is commonly implemented in other signalage in the area.

I do not think that in most intersections, the signals above your lane give you indications to do things that you are not permitted to do in that lane. I can think of lots of examples where the left turn arrow is on the left signal only, and no others where the left turn arrow is displayed all the way across (except when all the lanes can turn left). Or the red-straight-green-right you see sometimes, the green right is only displayed on the rightmost lane.

[kirisutogomen.livejournal.com]

Yeah, I have no idea if there are any other intersections using this ruleset. I drive north through that Mass/Cameron every time I leave your house, but I'd never noticed there being anything unusual about it.

[firstfrost.livejournal.com]

You wouldn't really notice the weirdness unless you were first in line - the left arrows are only there for about a second or two.

I did get an answer from hr_macgirl's person, and he said you and I were both right. :) You, because always have redundant signals for redundancy. Me, because that was a not a good place for the backup copy of the left arrow. It might move!