In a Wall Street Journal article entitled "Taxing for highways, paying for bike lanes"
The Highway Trust Fund now pays for a plethora of projects that have little to do with highways. According to a 2013 analysis by the Heritage Foundation, at least 20% of gas-tax revenues in recent years went toward other programs, from light rail to bike lanes to landscaping projects. Some funds even went toward establishing transportation museums.
So many things here:
1. As Heritage points out, transit was given $6 billion in 2010 and TA "which included pedestrian and bicycle paths and facilities, recreation trails, landscaping, environmental mitigation, and transportation museums." was given $3.1 billion over 2009-2011. Of course in 2010, $14.7 billion was transferred from the general fund to the HTF. So even if nothing had been spent on transit and TA, the gas tax still wasn't covering the cost of roads. By the transitive property, general funds were being used to shore up the HTF as well as pay for transit and TA programs. Making this explicit, instead of adding in the illusion of transit and TA coming from the HTF, wouldn't have changed anything substantive.
2. The Heritage study doesn't say that "at least 20% of gas-tax revenues" went towards other programs, in fact it says something other than that. It says that 16% goes to transit and that TA gets "2 percent set-aside of total highway funding," which, as stated above, is more than just "revenues" or even "gas-tax revenues."
3. The primary source of bike lane funding is likely local and state government, not TA.