Hi there I know guidance is still being developed but one item for consideration in it is how to handle a speed limit change mid segment. Should the segment be cut, no speed limit entered or other?


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*Updated to reflect correct terminology of "Cut"

nzahn1 wrote:I think you misunderstand the "threshold", the issue being debated is how close to another junction-node would you add an extra junction to change a speed limit. For example, you are traveling down the road at in a 30 mph speed zone, at 85' past an intersection, the speed limit changes to 40 mph. The question is: Do we want to add another junction node 85' away to change the speed, when the driver will cover that distance in less than 1.5 seconds.

Agreed, but if the speed limit is lowered approaching the intersection specifically to ensure that traffic is proceeding at a safe speed through the intersection, then it seems to me that an extra junction node is warranted before the intersection (at whatever location the sign is).

nzahn1 wrote:In addition, most speed limits are set in regulation/statute/code intersection to intersection, but maybe only enforceable after notice is given (posted sign). So do we assign speed limits where they actually change, or where signs are posted?

Seems to me that where the limits are only enforceable where posted, we should assign speed limits based on the signs giving appropriate notice of the limit (without adding "unnecessary" junction nodes).

DwarfLord wrote:We are hamstrung by not knowing how Waze plans

Waze plans?

DwarfLord wrote:Will they provide near-instantaneous alerts of speed-limit changes, demanding high precision from the Waze map?

This seems to me to be by far the least complicated implementation from the developers side. Without evidence to the contrary, it seems to me that this is what we should assume.

DwarfLord wrote:Will users come to expect this behavior, and begin aggressively flagging failures? Will the volunteer community end up in a scramble to add junction nodes for every speed limit sign in the world?

Flagging perceived speed limit failures and editors adding junction nodes at every speed limit sign they can find is going to happen; its just the way we are. There's only so much that wiki will do to change this. We might be able to change the channel of the river with the wiki, but we're not going to dam the river.

Fredo-p wrote:STOP, STOP, STOP!!!!! Since when did we and the waze app become traffic enforcement?

That's the argument that has been voiced for years whenever someone requested that speed limits be incorporated into the app. If it were the absolute truth, we wouldn't be mapping speed limits at all. But we are.

What about Toll Plazas? This question came up in the SF Bay Area.

Toll plazas often have official, legally-enforceable Speed Limit signs such as 5, 10, or 15 MPH compared with the freeway before and after them, which may be 55 or 65.

Some toll plazas may have separate lanes with dramatically different speed limits for drivers paying electronically versus with cash. One lane might be 5 MPH while a nearby lane might be 45 MPH.

What's the best way to deal with these? I'm sure Waze doesn't envision us drawing multiple lanes on the map for the different speed limits. But when the speed limit is undetermined (Waze won't know who is paying electronically versus cash) does it make sense to enter any speed limit at all?

What about even the simplest case where the speed limit for all drivers drops to 5 MPH for a very short distance? Should a short segment be inserted with the slower limit? Or should the limit be left blank? Or...?

herrchin wrote:What should be done with the middle segments at a box or partial-box junction? No speed limit?

Short answer: I don't know; I don't think anybody really does for sure.

Medium answer: for now, may as well leave speed limits blank anywhere the answer isn't obvious. Waze is preparing to cope with a LOT of blank speed limits; a few more won't make much difference.

Long answer: we don't know for sure HOW Waze is going to use the SL information. We can guess they will simply pass it along to the app user. But they could also -- if they wished -- do things like:

1. Offer potentially different routes and ETA estimates to drivers who state they are unwilling to exceed speed limits.

2. Build per-user profiles of speeding behavior. This in turn would allow Waze to customize route and ETA for each Wazer.

3. Flag areas where drivers habitually speed, and sell the data to planning agencies or law enforcement.

Because we don't know how Waze is going to use the speed limit data -- it seems unlikely to me that they will limit themselves simply to passing it through to the user verbatim -- I think we need to be careful about guessing what to do in confused areas, such as toll plazas with two or more speed limits, or intersections and small roundabouts.

wimvandierendonck wrote:If the distance to the crossing is above 20m you can. The exact value is dependent on your local community. (So you might check there)

Can you clarify if this 20-m threshold is from:

• Local law/police -- that is, a driver can legally continue at the previous speed limit for 20 m after a sign;
• Something Waze said in public (if so, where did they say this?);
• Something Waze said in private (if so, to whom did they say it? the Champs?); or
• Something your local community decided based on local ideas about how to use WME, but without any information from Waze and not based on how local authorities enforce speed limits (if so, could you identify your local community?)

Thanks. It is indeed a difficult question. My hope was to understand whether Waze had actually told somebody something in private somewhere (which of course happens all the time!) or, if not, where this 20-m number comes from and where exactly it applies.

I have no problem at all with a local community deciding on its editing practice! It just seems appropriate that a local editing practice be thoroughly labeled -- specifying the locality and justification -- when offered in a public forum. For example, one might say "in Southeast Lugash we have decided to use 20 m as interim guidance based on our understanding that Waze performance gradually degrades at inter-junction-node distances below 20 m". Or one might say "in Outer Raspur we have decided to use 100 m as interim guidance in an effort to limit proliferation of arguably unnecessary junction nodes".

I sure don't know what the right number is for the US or for anybody else. I would just like to understand, when a number is quoted, where it came from and where it applies.

CBenson wrote:Seems to me that where the limits are only enforceable where posted, we should assign speed limits based on the signs giving appropriate notice of the limit (without adding "unnecessary" junction nodes).

We are hamstrung by not knowing how Waze plans to present Speed Limit information to the user.

Will they provide near-instantaneous alerts of speed-limit changes, demanding high precision from the Waze map? Will users come to expect this behavior, and begin aggressively flagging failures? Will the volunteer community end up in a scramble to add junction nodes for every speed limit sign in the world?

Or will Waze treat this as a sort of background advisory, waiting for some period of time before alerting the driver that they may be speeding? This approach will demand much less effort from the volunteer community (and will surely result in FAR fewer URs).

It would be really helpful to know.

MC109SC wrote:When the speed limit becomes enforceable, decreases should never be late and increases should never be early.

This is a useful qualification, thanks.

We must bear in mind that, beyond some point, extra precision in placing junction nodes for speed limits buys us nothing.

Specifically, if Waze ends up displaying the speed limit, but not offering audio alerts, then precision will be relatively unimportant; the driver should be looking out the windshield not at the display.

Even if Waze does provide voice announcements for changes in speed limit (if they do, I'll probably be among the first users to try to shut them off) there is latency in voice announcements. This latency depends on the audio path among other things. For example I have seen up to 3 seconds' delay using a factory bluetooth system compared with direct audio. At 65mph that would be 87 meters.

In other words, even if we create a new junction node and put it within 1 m of the enforceable sign, and Waze issues a voice alert, a user with that audio path may not hear the alert until 87 m later. It may be an extreme case, but it illustrates the point that exacting precision in placing speed limits may have less value than we think.