WASHINGTON (AP) — Compromises on sticky environmental and safety issues enabled House and Senate negotiators to reach agreement Wednesday on a two-year bill to overhaul federal highway and transit programs.

Congressional aides were still writing the agreement into legislative language late Wednesday, as lawmakers faced a tight deadline. The government's ability to pay for transportation programs, and its power to levy federal gasoline and diesel taxes, expires on Saturday.

Details of the agreement have not been released, but House and Senate aides, speaking on condition of anonymity because the deal wasn't final, described key compromises. They include:

—House Republicans agreed to drop insistence that the government approve the Keystone XL oil pipeline and to block the Environmental Protection Agency from regulating ash generated by coal-fired power plants. Republicans said the pipeline, which would transport oil from Canada's tar sands to Port Arthur, Texas, would create jobs and lower U.S. gasoline prices. Opponents said it would have no impact on gas prices, and most of the oil will be shipped overseas.

Coal ash is used as an ingredient in some types of cement. It also contains a variety of toxic substances. Republicans wanted to let states decide how it should be regulated. Opponents of the proposal said a national standard is needed.

—The Senate agreed to House GOP demands that federal requirements for environmental impact studies of highway and transit construction projects be revised to speed up the time it takes to complete projects. Republicans argued that the 15 years on average that it takes to complete a major transportation project is too long. The compromise is aimed at cutting that time in half.

—The Senate agreed to effectively reduce money available for bike paths, pedestrian safety projects and other "transportation enhancements" by making them compete with other transportation programs for the same pool of funds. Republicans derided the program as wasting money on planting flowers. Supporters said that while highway landscaping was one project category eligible for funds, more than half the money is used for sidewalks, crosswalks, medians, bike lanes and other safety-related improvements. Cutting funding for biking and pedestrian projects was a high priority for House GOP freshmen, who said the money would be better spent on roads and bridges.

—The agreement includes language directing 80 percent of the Clean Water Act fines from the April 2010 oil spill in the Gulf of Mexico to restoration of communities in gulf states hard hit by the disaster. But the Senate agreed to the House GOP's demand that $1.4 billion for general land and water conservation be stripped from the measure.

—A safety provision that requires commercial trucks to be equipped with devices that keep track of how many hours drivers spend behind the wheel was retained in the bill despite a concerted lobbying effort by drivers who own their trucks to have it removed. The purpose of the devices is to keep drivers who haven't had enough rest off the road. The provision was supported by large commercial truck companies, safety advocates and labor unions.

—Also in response to a House GOP demand, the Senate dropped a provision that would have required automakers to equip cars with computer programs that record and save details of the vehicle's operation immediately before and after an accident. Safety advocates said the "event data recorders" would help accident investigators and improve safety. GOP lawmakers expressed concern the "black boxes" would be an invasion of motorists' privacy.