Bull**it environmental speed limits. Set at 60 MPH on 820 loop around Fort Worth where everybody cruises at 73 MPH or better except near end of month when Fort Worth cops need to meet their quotas by hassling white collar commuters (instead of rounding up the Mexican gangs and Katrina refugees plaguing Fort Worth). Hell, if lower speeds save so much gas set them at 10 MPH. Eco-fascists just love being in your face every chance they get-a big power trip for these watermelons.
Your comment reminds me that I need to qualify my earlier comment. Cops run a speed trap on the south end of George Bush (between I35 and the south toll plaza) near the end of each month. Richardson cops run a Sunday morning revenue operation on US75, weather permitting. (Primarily northbound, but they will nail a few southbound as they loop around).