Washington's Metro was one of the first transit systems in the US to allow bicycles on board, but not the first. Port Authority Trans-Hudson (PATH) in New Jersey, started its bike-on-rail program in 1962 and BART started its sometime prior to 1980.
BART's program enjoyed strong public support; by 1980, BART had issued more than 9,000 bike-on-rail permits. Community support and the excellent safety record of the program prompted BART to relax restrictions on the bike-on-rail service and permits were made available through the mail. By 1984, the number of permits had more than tripled to 28,000; this had grown to 71,000 permits by 1992. BART's success prompted other rail systems to institute bike-on-rail programs.
A 1988 Washington Post article claimed that 1980 is when Metro started it's Bikes-on-Rail program, which would make them the 3rd system to have a "Bike-on-rail" program.
Since 1980, Metro has allowed bicycles on the subway system, under numerous restrictions that favor local adult residents, discourage tourists and keep out children.
Metro decided "for safety reasons to limit participation" in its "Bike-on-Rail" program, said bicycle coordinator Randy Howes.
But according to a contemporaneous article in the DC Gazette it actually started in mid-1981, as a six month pilot. It was made permanent in January of 1981. At that time, cyclists needed a $10 permit that was good for 2 years, and that would allow them to use the system on weekends and some holidays. Getting a permit required a 30 minute training and passing a test. I'm not sure if that was still early enough to be 3rd or not.
By 1988, Bikes were allowed on the trains on weekends and holidays (except July Fourth), and after 7 p.m. on weekdays. Back then, you had to have a permit, which required learning the rules and taking a simple 17-question test (By 1992, only 3 people had ever failed it, one because he didn't speak English and one because he couldn't read). And only one person had ever had their permit revoked (for riding on the platform). Permits cost $15 and were valid for 5 years. Kids under 12 couldn't bring their bikes on and you had to use the last car in the train.
Metro board members voted to allow bicycles on trains between 10 a.m. and 2 p.m. weekdays for a six-month trial beginning Aug. 1.
The more liberal policy reflects the influence of General Manager Lawrence G. Reuter. Previous Metro general managers have been cool to the idea of extending subway access to bicyclists. Reuter came to Metro from the San Jose transit agency, which allows bicycles on trolleys and some buses for most of the day.
[Sidenote: From this article, I learned that MARTA allows bikes on its trains all day, every day, and it still does 22 years later. In case that's ever relevant].
In 1998, after another six-month trial, they got rid of the permit system.
In 2001, the hours were extended again. This time allowing bike on before 7am, and until as late as 4pm. This is the system we have today.
[In 2003, they added bike racks to their buses]