I'm interested in training for the Sado Triathlon in September, and the main thing I've heard regarding injuries/health risks is the risk of injury trying to train on the road bike in the greater Tokyo area. Where/How do you train for long distance biking without dealing with heaps of cars, bad roads, sharp bends and steep inclines/declines?

The actual route at the Sado Triathlon is pretty flat and straight and is closed to cars, so I'm not worried about that, but I'd like some helpful advice and/or locations for training! (I live in Kawasaki city, if that helps)

Well, it's been quite a while since I lived in Tokyo (1992..), but back then I actually was able to sucessfully train for the Death Ride. The key was to get out of the city as early as possible. As I recall the sun would come up REALLY early... like ~4:00am. The best escape route I had was the Tamagawa (or Tama) river. This had bike paths on the east side for quite a ways, and could get me into the countryside and/or mountains to the north. As I recall, the Kawasaki City is on the west side of the Tamagawa. The nightmare was always on the return though, as I would need to ride back to Sangenjaya from the river in the afternoon when the traffic, vehicular, pedestrian, and bicycle was beyond belief. And by bicycle traffic I don't mean other "roadies", but typically moms with groceries in baskets and kids on the back, weaving down the sidewalks.

Good Luck

I live about 1 /12 hours away from Tokyo and right off the river he mentioned. The river path is good for a recovery ride, but for training it is a little tricky because of all of the people (walkers, road bikers, kids...). We do rides near Yokota Air Base (where I am stationed). Leaving the base, we go through Fussa City, cross the river and take route 411 up to Lake Okatama, then up and over the mountain, round trip it is 71 miles. If you don't want to go up and over the mountains...you can stay on 411 and do an out and back...making it any distance you want while keeping the climb to about 6%. If you want to ride up here let me know, and we can meet up for some rides so you can learn the area. Traffic is not too bad either.
Matt

Congestion on the Tamagawa path varies with the day and time, with weekends not surprisingly the most crowded. You can still train at moderate speed, but it's nerve-wracking to say the least. The Arakawa path is much wider and more amenable to riding, but unfortunately for you is on the opposite side of central Tokyo. You could, of course, bag your bike and take the Metro over there (Minami-Sunamachi on the Tozai line, for example).

Can't help ya with Tokyo, but it's the same situation in Osaka. Get to a river, get out of the city ASAP.

From Kawasaki, you might consider the following route, though you'd still have to climb Mt. Takao:
http://www.bikely.com/maps/bike-path/Takao-Spring-07

As some other posters have stated, the rivers draining into Tokyo Bay are the best (only) bet. I live next to the Edogawa River in east Tokyo but I really wouldn't consider it satisfactory. The pedestrians and other cyclists are clueless, totally lacking in road sense or consideration for other users. They walk three/four abreast, stop to chat in huddled groups and seldom show any lane discipline. One other problem is ongoing construction work-Japan is riddled by pork-barrel construction schemes and local municipalities are constantly upgrading/re-building river banks and paths so you often find yourself bouncing over gravel or wooden boards or metal plates.
I too would recommend the Arakawa River south as far as Kita Senju (a major railhead) but use the path on the West Bank as the other side is a building site right now.
You might want to ask around the specialist bike shops if your Japanese is up to it. Try Sekiya- it's in Nishi Koyama, not far from Meguro. They're also just about the cheapest place in central Tokyo for high end bikes and components. Good luck!

http://www.sekiya-cycle.com/index.htm