Goofy Routing

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Re: Goofy Routing

Postby CBenson » Fri Jan 31, 2014 2:50 pm

I agree that this looks like the left turn issue from the other thread. I think this routing is a problem, but I will mention a couple of things.
scerruti wrote:The purple path avoids a left at a red light in favor of a left at a stop sign, but it still has to wait for the very same light. And since the left turn light turns green after the straight through traffic in the same direction stops you are almost guaranteed to get the left turn at the light before the straight through.

I don't think it matters that the left turn comes after the green for the other direction unless the other lights in the area are coordinated with this light. Won't you essentially hit the light a random time in the sequence.

scerruti wrote:What bothers me about this is that if I didn't know where I was going I would just blindly follow the instructions which are clearly stupid. Any suggestions?

I usually do blindly follow the instruction and can say that after taking the route a couple times, waze stops giving me the clearly stupid routes. So my suggestion is to take the route a couple of times so waze has the data it need to route well.


scerruti wrote:Am I helping to cause this by pulling up the alternate routes screen multiple times during my six mile drive?

I doubt it, as these issues are reported by many users and I doubt most users are pulling up the alternate route screen.
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Re: Goofy Routing

Postby CBenson » Fri Jan 31, 2014 4:36 pm

scerruti wrote:The vast majority of time for this light the East/West light is green. In most cases if you are turning left from the East or if you are travelling South you will have to stop for the light. At most times of day the left turn light to turn from westbound Oceanside to southbound Crouch will turn green before the light turns green to allow the Crouch traffic to travel straight across. Therefore in the vast majority of cases the proposed route will result in a longer wait time at the light, specifically the length of time the left turn light is green (and possibly the time the left turn from Crouch northbound to Oceanside westbound is green).

This still doesn't make sense to me. If you approach the intersection from the west to turn south when the light is red for the cross traffic you will have to wait for both the cross-traffic and the east/west green before you get the green turn arrow, correct? I don't see why it would matter whether the cross-traffic green comes before of after the green turn arrow, the left turners still have to wait during red light, so the averages that waze seem to use should be essentially the same.


scerruti wrote:The only time this proposed route would be shorter would be if you hit the intersection when the traffic on Oceanside was stopped at the red light. However, since the proposed route is longer and involves a stop sign I suspect you would miss that cycle of the light and wait even longer.

Sometimes you'd miss it, sometimes you'd hit the green. If the green for crossing is longer than the left turn arrow, then you should hit the green more often than hitting the green to turn left (in the absence of other traffic). Presumably waze calculates on average it is faster to go around the block. The problems are 1) waze may not have good data for say the left at the stop sign and 2) averages aren't really that helpful when the difference in the averages is well within the deviation of either route.
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Re: Goofy Routing

Postby CBenson » Fri Jan 31, 2014 10:32 pm

scerruti wrote:Assume two hypothetical drivers. D1 goes straight, D2 turns. The only way that D2 beats D1 is if D2 arrives prior to Ta and Tx < (Tc+Td).

I have a few problems with this.

1) What you are essentially saying is that D2 will arrive at the light Tx later than D1. But presuming that at T0 the light could be at any point in the cycle, the actual point in the cycle when they reach the light will be random. As long as Td>Tb then, in the absence of traffic, on average it is going to take D2 less time to clear the intersection than D1. The question is whether the difference in the times to clear the intersection is greater than Tx or not.

2) I don't think Waze is calculating the probability that for any T0 in the light cycle D2 will be faster than D1. Rather waze seems to be averaging the times. So even if D1 is faster more often, if D2 is so much faster when it is faster that the average for D2 is faster, then I think waze chooses D2.

3) None of this really matters in the hypothetical no traffic situation. I agree that that if Ta is much greater than Tb, Tc and Td, then the average time for D2 to clear the intersection is unlikely to be Tx faster than the average time for D1 to clear intersection. But all this changes if many people are turning left from Oceanside to Crouch and there is little traffic on Crouch. Then you may bypass the queue by going around the block. Assuming that waze has valid data for Tm, it seems to me that waze could be detecting traffic waiting to turn left.

4) I still suspect that waze is underestimating Tm and that if D2 is driven a few times, waze will learn that Tm is greater and stop routing this way.
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Re: Goofy Routing

Postby davipt » Thu Jan 30, 2014 11:12 pm

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Goofy Routing

Postby SlowlySlowly » Thu Jan 30, 2014 10:33 pm

This is my UR from today.

detour.png
detour.png (33.08 KiB) Viewed 504 times


This is the kind of thing that caused me to uninstall Waze a couple of years ago. I am driving through this intersection 2 or 3 times day and have been since I installed Waze again a week ago (except Weekends).

The purple path avoids a left at a red light in favor of a left at a stop sign, but it still has to wait for the very same light. And since the left turn light turns green after the straight through traffic in the same direction stops you are almost guaranteed to get the left turn at the light before the straight through.

There was no traffic at this time and no incidents visible on the map.

What bothers me about this is that if I didn't know where I was going I would just blindly follow the instructions which are clearly stupid. Any suggestions?

Am I helping to cause this by pulling up the alternate routes screen multiple times during my six mile drive?
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Re: Goofy Routing

Postby SlowlySlowly » Fri Jan 31, 2014 3:19 am

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Re: Goofy Routing

Postby SlowlySlowly » Fri Jan 31, 2014 4:29 am

I moved this to the end of this thread.
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Re: Goofy Routing

Postby SlowlySlowly » Fri Jan 31, 2014 4:01 pm

CBenson wrote:
scerruti wrote:The purple path avoids a left at a red light in favor of a left at a stop sign, but it still has to wait for the very same light. And since the left turn light turns green after the straight through traffic in the same direction stops you are almost guaranteed to get the left turn at the light before the straight through.

I don't think it matters that the left turn comes after the green for the other direction unless the other lights in the area are coordinated with this light. Won't you essentially hit the light a random time in the sequence.


The vast majority of time for this light the East/West light is green. In most cases if you are turning left from the East or if you are travelling South you will have to stop for the light. At most times of day the left turn light to turn from westbound Oceanside to southbound Crouch will turn green before the light turns green to allow the Crouch traffic to travel straight across. Therefore in the vast majority of cases the proposed route will result in a longer wait time at the light, specifically the length of time the left turn light is green (and possibly the time the left turn from Crouch northbound to Oceanside westbound is green). The only time this proposed route would be shorter would be if you hit the intersection when the traffic on Oceanside was stopped at the red light. However, since the proposed route is longer and involves a stop sign I suspect you would miss that cycle of the light and wait even longer.
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Re: Goofy Routing

Postby SlowlySlowly » Fri Jan 31, 2014 6:51 pm

I knew I was being unclear. Let me attempt anew.

The driver is approaching the fork with two choices, straight or right. The question is, will the state of the light ever make taking the right more attractive?

Let's code the light timing as follows:
Oceanside Straight: OS
Oceanside Turn: OT
Crouch Straight: CS
Crouch Turn: CT
Cycle TimeOSOTCTCS
TaGreenRedRedRed
TbGreenGreenRedRed
TcRedRedGreenRed
TdRedRedRedGreen


At T0 the driver arrives at the decision point. The longest cycle is Ta so there is a good probability that the driver will need to wait some fraction of Ta and then make the turn at Tb. In the worst case the driver arrives at the intersection at Tc and ends up waiting for a whole light cycle to make the turn (Tc+Td+Ta).

Let Tn be the amount of time for the driver to arrive at the intersection without the turn and Tm be the amount of time it takes to go through the stop sign and arrive at the intersection after the right turn. The driver immediately incurs a penalty Tx = (Tm - Tn). In the best case the driver arrives at the light during Td.

Assume two hypothetical drivers. D1 goes straight, D2 turns. The only way that D2 beats D1 is if D2 arrives prior to Ta and Tx < (Tc+Td).
The attachment timing.png is no longer available

So, because of the order of this light and the disproportionate length of Ta. The assumption that Tx is a large number (Google says 24 seconds) relative to the length of the light. The opportunities for D2 to ever be a faster route are probabilisticly low.
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