Official Taiwanese Highway website:http://www.freeway.gov.tw/english/Publish.aspx?cnid=1156
How to drive in Taiwan: http://en.wikipedia.org/wiki/Highway_system_in_Taiwan
<--The sign you will see that indicates a rest area (Service area). The signs usually also have English, so don't worry.
<- The Nantou Rest Area, the best rest area in Taiwan and the world.
Rest Areas: a Special and Under-Appreciated Part of Taiwan
Nowadays, with the invention of the Taiwanese Shinkansen High Speed Rail, no one takes road trips around Taiwan anymore. Why take a road trip when you can get to Kaohsiung in half the time? I am a proud Taiwanese that has never taken the High Speed Rail. Thats partially because of my family's cheapness and also, our realization of the meaningfulness in road trips. That meaningfulness is composed partially of those rest areas. The first time I encountered a rest area, I was tired and had "Ra ca Chnn" (Taiwanese for "Sore Butt") from driving so long. Suddenly, almost like a mirage in a desert (though Taiwan is the complete opposite of a desert), a huge mini mall appeared in the middle of nowhere. The parking lot was full of cars, and had those cool speakers that played music. They even had a counter to show you how many parking places were left.
Parking lot
Anyway, me and my parents stumbled into the mini mall to find a completely modern and shiny array of stores. Most of the stores had food tasting. The place resembled the malls of southern California, minus the movie theater. Restaurants selling Beef noodles and Taiwanese food lined the food court, and a huge aboriginal boat thing was hung from the ceiling
We ate lunch there and moved on, only to find a similar rest areas all over the place. By the end of the trip I grew familiar with most of the rest stops. Note: if you expect to visit all the rest stops, then make sure that you can afford to spend an extra hour on the road
Dining area @ Sihu
The biggest service area is Sihu (I think), which is actually a complex of buildings and various stores. http://www.freeway.gov.tw/english/Publish.aspx?cnid=1156&p=1581 or http://www.shihwu.com/
The Service area at Sihu is actually sponsored by the famous I-mei foods, a popular brand in Taiwan and Southern California (go to 99 Ranch Market and half the stuff there is I-mei).
Service areas are numerous and spread across Taiwan. There will always be a sign pointing to the service Area. The sign will probably be in English and Chinese. http://www.google.com/maps also shows all the rest areas, marked with a fork and Knife. Not all the service areas marked contain a minimall. Some are just bathrooms.

http://www.freeway.gov.tw/english/Publish.aspx?cnid=1156&p=971 Cingshui rest station in Taichung
singying Rest Area in Tainan
a starbucks in Rende Rest Area