Where do you live that it is illegal to ride on the sidewalk? In some European countries it is strictly illegal, but in most US states it is a state decision as to what the rules are. In Michigan it is not illegal, but frowned upon (i.e. you can do it in circumstances like you described). Still, I get yelled at all the time to ride on the sidewalk, even when I am going faster than traffic...
More than you wanted to know (For the state of Michigan at least):
Must a cyclist ride on the sidewalk? Is it legal? What about crosswalks?The MVC does not require bicyclists to ride on the sidewalk and we do not recommend it because of safety hazards to the bicyclist and other sidewalk users.
However, Section 257.660c of the MVC says:
(1) “An individual operating a bicycle upon a sidewalk or a pedestrian crosswalk shall yield the right-of-way to pedes-trians and shall give an audible signal before overtaking and passing a pedestrian.
(2) “An individual shall not operate a bicycle upon a sidewalk or a pedestrian crosswalk if that operation is prohibited by an official traffic control device.
(3) “An individual lawfully operating a bicycle upon a sidewalk or a pedestrian crosswalk has all of the rights and responsibilities applicable to a pedestrian using that sidewalk or crosswalk.”
Dangers of Sidewalk Riding — Remember that you are “invisible” on sidewalks! Cycling on sidewalks is VERY dangerous. Motorists are looking in the road; they are not looking for vehicles — like bikes, which may be moving at nearly traffic speed — on the sidewalk. They commonly don’t “see” you there, especially at driveways and intersections.Cyclists are not required to use bike paths or sidewalks. However, If you must ride on a sidewalk (and local ordinance permits):
• Yield to pedestrians and walk bikes in crowded areas.
• Provide an audible approach warning by calling out “Passing on your left,” or by ringing your bell.
• Watch for inattentive motorists; don’t assume they see you.
• Whenever possible, ride with the direction of traffic (on the right side of the road).
I've seen cyclists crunched when riding on sidewalk on the left side of the street. No motorist that I have ever seen (on this continent) stops before the sidewalk, or looks to the right when entering an intersection or crosswalk. Riding against the direction of traffic on the sidewalk is pretty dangerous.