Narrative:

[We were] taxiing out with east; then west ramp control. We received three taxi routing changes and three runway assignment changes. The last clearance we received was wb to wd to nr to nb to runway 15R. When reaching what we thought was wd the captain started the slight right turn. Ground called us and told us that we couldn't taxi there and to stop. The captain brought the aircraft to a smooth stop. We then asked ground what the issue was and they told us that we were on taxiway nr and there was a wingspan restriction. We then rechecked the taxi charts and realized where we were and also saw the note that stated no aircraft with a wingspan greater than 125 ft were allowed to use this taxiway.I asked ground what the plan was and they said airport operations personnel were on their way with a tug to push us back so we could continue on taxiway wb up to wd. The airport operations personnel arrived approximately 10 minutes later and were able to provide wingwalkers and ensure no vehicle traffic would be near our aircraft while we moved along nr. Building; fence and light pole clearances were not a factor; so it seems like the restriction is in place for vehicle traffic.once we moved north on taxiway nr and were clear; ground cleared us to runway 15R. During that conversation the ground controller stated that this happens quite frequently and understands that the taxiways aren't marked very well at that intersection. While approaching this taxiway; the captain and I were very comfortable with the taxiway as there seemed no way obstacles were a factor for wingtip or engine clearance. I believe this spaghetti bowl of taxiways should have a 'hot spot' circle highlighting the multiple clearances that are possible and the associated taxiway restrictions.

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Original NASA ASRS Text

Title: Following multiple revised taxi clearances at IAH the flight crew of a B767-300 found themselves on NR which is restricted for use by aircraft with wingspans greater than 125 FT.

Narrative: [We were] taxiing out with East; then West Ramp Control. We received three taxi routing changes and three runway assignment changes. The last clearance we received was WB to WD to NR to NB to Runway 15R. When reaching what we thought was WD the Captain started the slight right turn. Ground called us and told us that we couldn't taxi there and to stop. The Captain brought the aircraft to a smooth stop. We then asked Ground what the issue was and they told us that we were on Taxiway NR and there was a wingspan restriction. We then rechecked the taxi charts and realized where we were and also saw the note that stated no aircraft with a wingspan greater than 125 FT were allowed to use this taxiway.I asked Ground what the plan was and they said airport operations personnel were on their way with a tug to push us back so we could continue on taxiway WB up to WD. The airport operations personnel arrived approximately 10 minutes later and were able to provide wingwalkers and ensure no vehicle traffic would be near our aircraft while we moved along NR. Building; fence and light pole clearances were not a factor; so it seems like the restriction is in place for vehicle traffic.Once we moved North on Taxiway NR and were clear; Ground cleared us to Runway 15R. During that conversation the Ground Controller stated that this happens quite frequently and understands that the taxiways aren't marked very well at that intersection. While approaching this taxiway; the Captain and I were very comfortable with the taxiway as there seemed no way obstacles were a factor for wingtip or engine clearance. I believe this spaghetti bowl of taxiways should have a 'hot spot' circle highlighting the multiple clearances that are possible and the associated taxiway restrictions.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.