So, you want to add a little vroom to your bicycle. Here’s what state law says about that

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Trevor Hansen of Whatzz-Up Electric Bikes in University Place demonstrates how electric bicycles work.

Q: My son, who does not drive, would like to put a motor on a bicycle. Can you tell me what the law is regarding this on Tacoma streets? Is there a difference whether it is an electric or gas motor? — Linda

A: There is definitely a difference. Buckle up, the answer to this one’s a little complicated.

Let’s start small.

If Linda’s son just wants a little oomph for his bike, he could turn it into an electric-assisted bicycle, meaning he’d be able to go up to 20 mph and wouldn’t need a driver’s license (provided he’s over 16) or insurance. He also wouldn’t need a registration for this type of bike like he would a motorized vehicle, because the law considers it a bicycle still. In some cities you’ll see restaurant employees buzzing around delivering food on something similar to this. It’s a nice way to avoid the nuisance of parking.

State law defines an electric-assisted bicycle as a bicycle “with two or three wheels, a saddle, fully operative pedals for human propulsion, and an electric motor.” The electric-assisted bike’s motor can’t have a power output of more than 1,000 watts and can’t be able to go faster than 20 mph on level ground. It also can’t be capable of going faster than 20 mph when human power is added. It can go everywhere a bicycle can, but it can’t ride on sidewalks or limited-access highways.

If Linda’s son is at least 16, simply wants to buzz around town and doesn’t want to get a driver’s license, this could be a good option for him. He could go out and buy a small electric motor, attach it to his bike and be on his way.

Next up: Gas-powered motors.

This is where things get a little more complicated because the law treats something with a gas-powered motor more like a motor vehicle than a bicycle.

Let’s start with mopeds. If you attach to a bicycle a motor that is less than 50 cubic centimeters, it would land in the category of a moped. State law defines mopeds as having no more than three wheels. They also can’t go any faster than 30 mph. You can drive them places you’d drive a car, but not highways since you wouldn’t be able to reach highway speed.

You still don’t need insurance for one of these (in Washington, you don’t need insurance for a full-blown motorcycle either), but you have to register it like you would a car, and you need to display a valid license plate. You also need to meet other motor-vehicle requirements: two mirrors, brakes, controls, head light, tail light, horn, brake light, license plate light, muffler, etc. You also have to wear a helmet.

Anything with a gas motor that is larger than 50 cubic centimeters is considered a motorcycle, said Sgt. James Prouty of the Washington State Patrol. In this case, it doesn’t sound like that’s what Linda’s son is looking for.

The upshot: If Linda’s son wants to go that extra 10 mph, is willing to pay for registration and get a driver’s license, he might look into adding a gas motor to his bicycle (landing it in the category of a moped.) But if he doesn’t want to deal with the hassle, he could probably stick with an electric-assisted bicycle and be able to ride up to 20 mph.

Candice Ruud: 253-597-8441, @candiceruud