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Old November 29th, 2008, 03:17 AM   #161
J N Winkler
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Quote:
Originally Posted by Alex Von Königsberg View Post
European or not, this sign is more clear and informative than those old stippled-arrow ones. In California, I saw several of them, and I should say that putting broken lines inside them doesn't make any sense because driving at 120 km/h it is impossible to count them anyway.
There isn't much in the legibility issue except where optional lanes are concerned. (BTW, very few of these signs are used on roads subject to anything like a 120 km/h speed limit.) On the other hand, there are plenty of complex interchanges with left exits, exits in rapid succession, or sharp turns in the mainline where stippled-arrow diagrammatics are helpful in giving drivers advance warning of the layout. The one-arrow-per-lane diagrammatics as proposed by FHWA do not have this advantage. The Houston-style diagrammatics can be adapted more easily to serve this function because they are not required to have the lane arrows at 12' spacing or to be overhead-mounted, but they do have the disadvantages that tall signs are difficult to mount in overhead positions while ground-mounted signs can be obscured by large trucks.

The theory of reading stippled-arrow diagrammatics actually places little emphasis on counting the spaces between stipples. Instead, you are supposed first of all to look at where the arrowheads go, and also whether the arrow shafts bend in any particular direction, because those are hints as to lane continuity and horizontal alignment. Then, if the interchange looks like a conventional split, you check for a stipple which runs up to the divide between two arrow shafts, because that indicates whether you will be dealing with an optional lane or not. Lane assignment is normally handled by other signs which have downward-pointing arrows, and also by pavement markings.

I am in favor of one-arrow-per-lane diagrammatics being used in locations where they can function better than stippled-arrow diagrammatics; this is why I argued for both to be left as options in the MUTCD, with the engineer being given discretion to choose between the two.
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Old November 29th, 2008, 08:56 AM   #162
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J N Winkler, I am not sure how those stippled-arrow signs were used to indicate left exits or exits in rapid succession (have a sample picture?) However, on the West Coast, these signs were used only and only to indicate a splitting motorway - that is, at least two lanes going in each direction. The perfect example would be the place where I-580 splits from I-5 right before Tracy. This can be perfectly indicated by the new "European-style" signs proposed by the FHWA.
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Old November 29th, 2008, 12:42 PM   #163
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You have one of those where I-15 breaks off from I-84 in northern UT going at (I do beleve) 75 mph. Try counting all the little tiny black dashed lines then, haha.
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Old November 29th, 2008, 04:00 PM   #164
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Quote:
Originally Posted by Alex Von Königsberg View Post
J N Winkler, I am not sure how those stippled-arrow signs were used to indicate left exits or exits in rapid succession (have a sample picture?) However, on the West Coast, these signs were used only and only to indicate a splitting motorway - that is, at least two lanes going in each direction. The perfect example would be the place where I-580 splits from I-5 right before Tracy. This can be perfectly indicated by the new "European-style" signs proposed by the FHWA.
I do have plenty of pictures. Before I go on to show them, I need to point out that FHWA's proposed change would do two things: (1) eliminate the stippled-arrow diagrammatic altogether, and (2) remove the option to use diagrammatics of either kind at exits and splits without optional lanes. (An optional lane is a through lane which divides into two at a split or multi-lane exit.) So I am captioning these pictures according to whether the MUTCD would support usage of the signs shown if it were revised as FHWA proposes.

Exits in rapid succession



This sign is located along I-30 in downtown Fort Worth, Texas. Since neither of the two closely spaced exits involves an optional lane, this sign would not be supported under FHWA's proposal.

Left exits



This is the classic left-exit diagrammatic. Under FHWA's proposal, designers would have the option just of using a yellow (text-only) "LEFT EXIT" panel to indicate a left-exit condition without optional lane. (On this sign, "LEFT" on the exit tab appears on a yellow background. Drivers are also supposed to understand that the positioning of the exit tab on the left side of the sign means that the upcoming exit is on the left, but there is evidence that this convention is not widely understood because there are still many signs from the 1960's and 1970's with center-mounted exit tabs.)



This sign indicates a left exit which is also a lane drop without optional lane. Because there is no optional lane, no diagrammatic would be used in this location under FHWA's proposed rule. Note the use of a solid line running up to the split of the two arrow shafts, to emphasize the lane drop condition.



This sign indicates a multi-lane exit on the left which has an optional lane and an auxiliary lane which opens on the left immediately before the exit. Because this exit has an optional lane, a one-arrow-per-lane diagrammatic could be used under FHWA's proposal. But FHWA's design does not have the flexibility of indicating an auxiliary lane which opens to the left. This creates the risk of driver confusion since the number of lanes at the exit won't match the lanes shown on the sign. (This use of chamfering on the stippled-arrow diagrammatic to indicate an auxiliary lane is far from unique; other locations in Michigan have similar diagrammatics.)



There is no optional lane on this sign, so no diagrammatic would be used under FHWA's proposal. But notice how the curvature of the arrows gives drivers advance warning that the mainline curves after the exit.

Unusual geometry (or geometry which violates driver expectancy) through or immediately after the exit



Here the mainline curves to the left while the exit ramp goes straight ahead. Under FHWA's proposal this situation would qualify for a one-arrow-per-lane diagrammatic, but mainly because the exit has an optional lane.



The situation is similar to that shown in the preceding picture, but without optional lane--meaning no sign under the proposed rule.

"Standard" splits



This is the stereotypical split diagrammatic, with optional lane. I am generally sympathetic to the argument that signs of this kind should be replaced with one-arrow-per-lane diagrammatics which clearly show the optional lane with a double-headed arrow, particularly since the interchange has no unusual geometric characteristics which could not be communicated equally well with lane arrows.

Moving on to your examples, there are actually examples of stippled-arrow diagrammatics which are used for left exits on the West Coast. I believe I-84 approaching the Multnomah Falls exit from the east has one.

The I-5/I-580 split near Tracy is in Caltrans District 10. Its neighbor to the north, Caltrans District 3, does use one-arrow-per-lane diagrammatics. (I think it is the only Caltrans district which does.) However, its splits are well-behaved in terms both of geometry and exit frequency.
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Old November 29th, 2008, 04:24 PM   #165
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Left exit? You mean you have multiple lane motorways where lanes branch off from the inner lane?
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Old November 29th, 2008, 05:05 PM   #166
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Left exit? You mean you have multiple lane motorways where lanes branch off from the inner lane?
Yup! We also have freeways which curve sharply in the middle of interchanges.

As a general rule, when two motorways cross, most drivers expect the through lanes of the crossing motorways either to remain straight or to have no more curvature than would be expected based on the terrain away from the interchange. This convention has been observed more consistently in Europe because European highway agencies have historically had a much sharper focus on building rural motorway networks.

In the US, on the other hand, there has been a very heavy secondary focus on bringing freeways into cities, to get more use out of rural freeway mileage and also to develop car-commuting infrastructure within densely populated urban areas. This has resulted in a lot of interchanges being built with left exits and sharp mainline curves partly to minimize demolition and save money on bridge construction. Left exits are now heavily discouraged in current design guidance, but there are still plenty of interchanges which have them and they will need effective signing until they are reconstructed.
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Old November 29th, 2008, 05:13 PM   #167
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Originally Posted by J N Winkler View Post
Yup! We also have freeways which curve sharply in the middle of interchanges.
Safety wasnt an issue back then? What if a slow driver wants to get off at left exit,through faster traffic in the left lane? Or a truck?
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Old November 29th, 2008, 05:56 PM   #168
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Safety wasn't an issue back then? What if a slow driver wants to get off at left exit, through faster traffic in the left lane? Or a truck?
The safety consequences were not well understood until later. The implicit assumption behind these interchange designs was also that traffic volumes would remain low enough that it would be relatively easy for slower traffic to move left to make the required maneuvers. Operational considerations now receive much higher priority and so left exits are very rare in new construction.
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Old November 29th, 2008, 06:32 PM   #169
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Left exit? You mean you have multiple lane motorways where lanes branch off from the inner lane?
It happens sporadic in Europe too.
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Old November 29th, 2008, 06:33 PM   #170
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AFAIK there's only one in the Netherlands, on the A2 near Eindhoven.

-edit- It's over here. It doesn't look like a real exit, more like an on and off ramp leading to a roundabout.
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Old November 29th, 2008, 10:43 PM   #171
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Yay! Toledo.
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Old November 30th, 2008, 01:24 AM   #172
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Late Saturday afternoon in Lebanon County, Pennsylvania. Traffic was all but stopped as America "resets" after the Thanksgiving holiday- traditionally one of the busiest travel days all year long in the US....AND we see that I-81 curves to the right while a left exit gets you to I-78 which begins at this junction...the fact that 81 makes a turn to the right is not on display with this sign for some reason.


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Old November 30th, 2008, 10:11 AM   #173
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Quote:
Originally Posted by Gil View Post
I think the reasoning why North America hasn't adopted the European-style blue signage is that here blue has a different significance.

Red signs are regulatory (stop, do not enter, etc.)
Orange signs are for construction or temporary (detours)
Yellow signs are cautionary
Green signs are for information
Blue signs are institutional (schools, hospitals, etc.)
Brown signs are touristic (information, gas stations, restaurants, hotels, etc.)
Black and white signs are obligatory (speed limit, one way, etc.)
As stated, the BLUE signs give the info, gas, business stuff, at least here in WI. Brown is reserved for parks/historical/recreation.



Anywho, I like most of the changes, but do we really need one way signs at the end of a FREEWAY ONRAMP?! This seems like a redundant waste. It's not like these onramps encourage anyone to turn into oncoming traffic.

They are putting YIELD signs at the end of freeway onramps on US-41 now, which is good because technically you're required to yield.


One last note, I haven't seen a DIVIDED HIGHWAY text sign in forever. They've all gone to picture signs here.
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Old November 30th, 2008, 04:41 PM   #174
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Shark's teeth have come to my neighborhood, at the only proper roundabout we have. It'll be interesting to see if they start appearing at other places as well.
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Old December 1st, 2008, 12:11 AM   #175
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If they just started replacing wasteful STOPs with efficient YIELDs, then we would see shark teeth everywhere.
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Old December 1st, 2008, 07:59 PM   #176
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Quote:
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Left exit? You mean you have multiple lane motorways where lanes branch off from the inner lane?
Is it really an exit, or it's a junction? If it's a junction, I don't see a problem here. Even an exit wouldn't be a safety issue, just not handy.
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Old December 1st, 2008, 08:16 PM   #177
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That looks like it could be quite dangerous. Look at the short distance over which entering traffic from I-290 has to merge across I-90 traffic wanting the first of those exits.
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Old December 2nd, 2008, 02:00 AM   #178
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Actually, the photo is taken from a very high view (probably from a helicopter). Traffic coming from the Eisenhower has its own lane that's not exit only. But for Traffic on the Kennedy, there's still plenty of time to switch over one lane before the exit.
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Old December 2nd, 2008, 02:21 AM   #179
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Moderator, can you delete the "proposed" in the thread title?
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Old December 2nd, 2008, 01:33 PM   #180
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What, they already approved these changes? AFAIK, they did not enact them yet because they are still reviewing the public comments. So, the title stays.
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