The southbound 495 Express lanes running next to the outer loop of the Beltway near I-66. On I-66, the beloved left exit lane eastbound for the northbound Beltway has been taken for use only by the HOT lanes. (Tracy A. Woodward/THE WASHINGTON POST)

Here’s what you need to know before getting in the 495 Express Lanes:

You must have an E-ZPass transponder. You can ride for free if you have both three people and an “E-ZPass Flex” transponder, a new model designed just for this project. You can get either transponder online here or in person at the Tysons DMV or service center in Herndon. Here is a very handy users guide by The Post’s Dr. Gridlock. Here is the HOT Lanes website.

The average cost of a trip will be between $3 and $6, depending both on how far you drive and the rate at the moment. But once you enter, the rate is locked in, and Dr. Gridlock says you are guaranteed at least a 45 mph drive. With the tolls changing according to the traffic at the moment, the HOT lanes could become the ultimate live example of free market economics. When the traffic controllers want more cars in the HOT lanes, they lower the price. When they want fewer cars, they raise the price. How high can they go? How much will you pay?

Speaking of pay, the tolls won’t be a money-maker for Virginia. The private companies Transurban and Fluor paid $2 billion to build the thing, and they’ll collect the toll money. But the Virginia State Police will be enforcing the traffic laws, for the income that brings in, including counting heads for those who want the “free carpool” status. (You must have three to ride for free. Hey, I’m copyrighting that.) The state police will be out this weekend in heavy enforcement mode to lay down the law early on.

With a similar project scheduled for I-95, everyone’s anxious to see just how this will work. There are concerns about how it will affect the American Legion Bridge and the traffic into and out of Maryland. Will it make the Beltway in Virginia more user friendly? We’ll see.

Here’s an explanatory video from the Hot lanes folks. Be sure to note the animation of cars cruising along the Inner Loop, while cheapo losers like me sit and watch in the free lanes.