Hacker News Reader

Comment by fedd | Hacker News Reader

they'd better invent 'minimize number of left turns', novice drivers would thank them

I wonder if UPS's existing "minimize number of left turns" navigation programs would constitute prior art?

you mean it's already invented? than it should. (i just never met this function in programs i used)

UPS uses this in the direction software their delivery vans use. minimization of left turns means the vans get everywhere faster and more packages are delivered in a given day.

I wish the US/state governments would do the same thing. I hate how the green left-turn arrow is the first thing to light at a stoplight. This penalizes efficiency and rewards a behavior that costs us all time and energy.

Why is it like this? The only valid reason I can think of is that turn lanes would tend to back up at most lights in busy cities. I would think correcting this behavior would help reduce the number of vehicles turning, to offset the backup.

You should check out the "Michigan left" which is being increasingly implemented around the country. A Michigan left prevents backup by having people turn right and then do a U-turn further down the road at a designated area.

Thanks for the concept epikur! This is better, but it seems this design would not work on very busy roads. You would never get a chance to cross oncoming traffic due to the volume.

This does seem perfect for most Midwestern highways where space is not really a concern and traffic is relatively light.

They installed one of these a few years ago where I live. Each U-turn area gets its own traffic light in addition to the light at the grade crossing; I don't drive through there often enough to know how the patterns are synchronized for the different lights.

For one highway and one non-highway, check out SPUIs: http://www.youtube.com/watch?v=mwpoPQ1SPJU

UPS considers it highly proprietary, so I'm not surprised that you haven't come across their implementation.

I had some customers who used it (Anheuser-Busch has some weird licensing partnership that their distributors get it for free-ish). So you CAN get it, if you have the money.

Just take Dijkstra's Algorithm (or possibly A* if you want to try to optimize the runtime performance) and give a higher cost to edges in your map that correspond to left turns. Now it's just a matter of tuning the additional weight added to suit your preference. You won't get the shortest distance any more, just the "cheapest" path in terms of the distance/left-turn weight; if you find you have to go too far out of your way to avoid left turns, you may want to reduce the added weight so you can make a few more left turns without going so far away. For example, you probably don't want to go 10 miles down the freeway and another 10 back to avoid a single left turn on what would otherwise be a 5 minute drive, but maybe you'd instead be willing to drive a 1/2 mile to avoid a left turn that you'd otherwise have had routed -- so route the left turn as whatever distance it would be plus 1/2 mile additional cost.

While I can't be sure, I believe that my TomTom Go 730 gives left turns a higher penalty than right turns when calculating a route.

I've seen it pick different roads to go A->B than to go B->A where the only reason I could discern for the difference was minimizing the number of left turns.

i thought i suggested something new for them to patent :(

Not to discount your possibility, but interestingly enough it's possible there are bugs in the mapping data.

See http://testoptimal.com/ref/starwest-2006-mbt-tutorial.pdf, page 99 for a neat example.

It's sort of ironic, I remember reading a much more in-depth paper from Harry about this specific work, but I can't find it. :-/

It might be minimizing driving time, which would in fact give preference to right turns over left, since you often have to wait for left turns.

I remember seeing a paper that suggested outlawing all left turns except onto cul de secs or where at least one road is one way would shorten driving times for everyone. Every time I get stuck behind a huge long line of jerks trying to turn left I think of that and seethe.

Reply on news.ycombinator.com