I commute home on the Katy Trail some evenings (like tonight), but I'd actually recommend taking the Santa Fe Trail up to the lake. The Sheraton is on the east side of downtown, so its a little closer to that trailhead. Also, the Katy Trail doesn't directly connect to the lake, so you have to cut through neighborhood streets for a few miles between the trail and the lake. The ride from the Katy Trail to the lake would require a second portion of neighborhood streets and 4 bigger intersections during rush hour traffic, only 2 of which have a stoplight to help you cross. The Santa Fe Trail ties directly into the White Rock Lake roads/trails so you can ride pretty much non stop once you get on it.
The lake itself has roads looping and a few sections of bike path. If you go the Santa Fe route, then it will suddenly merge you onto the White Rock Lake trail after a bridge. After about 3/4 of a mile you will hit a parking lot where you can either stay on that trail or cut over to the road looping the lake. Most runners are on the trail and most bikes are on the road.
http://www.mapmyride.com/...-lake-route-55183758
Edit to add a link mapping the Sheraton to the T.P Hill parking lot. That may be easier to see how to get to the trailhead.
The lake itself has roads looping and a few sections of bike path. If you go the Santa Fe route, then it will suddenly merge you onto the White Rock Lake trail after a bridge. After about 3/4 of a mile you will hit a parking lot where you can either stay on that trail or cut over to the road looping the lake. Most runners are on the trail and most bikes are on the road.
http://www.mapmyride.com/...-lake-route-55183758
Edit to add a link mapping the Sheraton to the T.P Hill parking lot. That may be easier to see how to get to the trailhead.