Wrong again. The Southwest Freeway in Houston is an 8-lane road for most of its length between downtown and the outlying suburbs. It drops to 6 in some construction zones at present, including one just outside of downtown and several near sugarland. There is also a brief segment of 10 lanes when the extended onramps are included near its intersection w/ 610. This predominantly 8-lane Southwest Freeway is also one of Houston's busiest and the most recent estimates suggest it carries about 390,000 vehicles a day on weekdays.
Total miles is irrelevant. All that matters is the vehicles going over any 1 mile of road to compare to per mile costs.
Wrong again. If commuters travel further in a given city they use more highway space and with it more gasoline. Since highways don't fluctuate in length from day to day they may be considered a constant. 100,000 commuters travelling 30 miles on Highway X a day use up more gasoline than 100,000 commuters travelling 2 miles on Highway X a day. Since Highway X and its original construction costs remain the same whether they travel 30 or 2 miles a day, any measure of gasoline revenues generated by that freeway MUST take the commute length into account. Why? Because longer commutes generate more tax revenue even though the freeway's construction cost stays constant be it used for long or short commutes. Otherwise you introduce a severe distortion that underestimates longer commutes and cities with greater highway usage.
Driving on freeways is by definition not city driving. City driving is driving on streets with stoplights.
You must not visit Houston during rush hour very often then. To get the sticker rated mpg figure for "freeway" driving one has to drive on a relatively uncongested and smooth flowing freeway. Anything less pushes you closer to the city rating, and Houston's congestion does just that. I can testify from experience when I drove Houston's freeways as a commuter for a previous job. My car at the time was rated 23 freeway and 18 city. When I drove to San Antonio or Austin I got about 23 freeway. When I drove to work every day on Houston's freeways I got between 18 and 19 mpg. So once again, you severely overestimate the mpg expectations for our freeway system.
Using your numbers, this implies really high gas taxes. 390,000 vehicles * $0.40 per gallon / 17 miles per gallon = $9200 per day = $3.36 million per year.
Your equation is flawed because it leaves out trip length. 390,000 vehicles travelling a 20 mile highway commute on average is substantially different than 390,000 vehicles travelling a 3 mile highway commute on average. Houston's drivers come closer to the former number. When you figure in that those 390,000 vehicles travel about 20 miles each on the Southwest freeway (which is, after all, the AVERAGE trip length for a given commuter, meaning it is the sum of all the trip lengths divided by all the vehicles) they end up paying more. Let's use another example for clarification purposes:
We'll take the gas tax at 40 cents a gallon and say that each car gets 20 mpg. That means for every 20 miles travelled a driver pays 40 cents in taxes. Now if there are 390,000 drivers on the southwest freeway a day and the AVERAGE commute for each driver is 20 miles, that also means the average driver uses a gallon of gas per commute and thus pays 40 cents in taxes. If 390,000 drivers pay $.40 in taxes a day that means $156,000 in taxes are collected on that highway each day. Times 365 days that gives us a little over $56 million in revenue for that entire highway per year (I know, taking weekends into consideration gives us a little bit less but just to keep things simple we'll stay at 56).
Now apply that to the I-10 stats: 37.6 miles per day, 390,000 commuters, and 17 mpg at $.40 per gallon in tax. That gives us a use rate of 2.21 gallons a day, or 88 cents in tax per commuter. Times it by 390,000 and we get $345,035 a day (My apologies and please disregard the previous $800,000 figure I gave you - I doubled the commute length thinking it was 40 miles each way when on second glance at the figure that is the total round trip). Multiply that by 365 and we have about $126 million a year, or about $3.15 million per mile per year on a 40 mile highway. Subtract the maintanence from that and you get revenues of about $3 million a mile, which recovers construction costs @ $20 million a mile (current I-10 estimates say $800 million for the expansion's construction costs over 40 miles = $20 million a mile) in about 7 or 8 years.
They are accurate for freeways up here.
They may or may not be, but we're talking about Houston freeways, not Pennsylvania.
No, you seem to totally misunderstand the point of the exercise. If we take the cost of constructing a mile of freeway as a constant per mile, the total length is irrelevant. The cars passing over any given mile upon it must pay for that mile. Saying a 30 mile freeway makes more money than a 5 mile one is besides the point. It may make six times as much, but obviously it also costs six times as long. Unit costs and revenues are identical.
Multiply that by 365 and we have about $126 million a year, or about $3.15 million per mile per year on a 40 mile highway. Subtract the maintanence from that and you get revenues of about $3 million a mile, which recovers construction costs @ $20 million a mile (current I-10 estimates say $800 million for the expansion's construction costs over 40 miles = $20 million a mile) in about 7 or 8 years.
Is the construction being financed with revenue bonds (normal method of construction of public works)? If so, you need to add the interest charges. Presumably the property underneath the road was once privately owned. You need to add on the foregone property tax revenue on that land. You need to add in the cost of policing the road and responding to accidents and incidents. Lastly, is the construction estimate in current year dollars, or year of expenditure?
I will grant the basic point - freeways in Houston are very heavily used but cheap to construct and therefore generate an atypical amount of money versus what occurs elsewhere in the country.