DENVER -- Five years of around-the-clock construction and $1.75 billion later, the T-REX project wraps up major work Tuesday.

At 10 a.m., Gov. Bill Owens will pick up the final orange cones to open the northbound off-ramp at Downing Street. That act, akin to a ribbon cutting, will mark the official completion of the 17 miles of widened and improved highway, including about five miles on Interstate 225.

The only major roadwork that isn't done is an emergency-access ramp to I-25 northbound at the Belleview Avenue entrance. That project, added because of a last-minute demand from the Denver Fire Department, shouldn't affect drivers too much.

Major construction on the light-rail system is complete, but it won't open until Nov. 17, following a mandatory testing period by RTD.

T-REX was built for one reason: the old Valley Highway - I-25's name before it was I-25 - couldn't handle the traffic anymore.

I-25 was a perfectly functional highway for the Denver of the 1960s: Three lanes in each direction, graceful grassy slopes along a stretch called The Narrows, a huge lazy cloverleaf interchange at University Boulevard, a death-defying left-lane frenzy of merging traffic at the I-225 junction.

Some people in south Denver have renamed The Narrows the "Grand Canyon of Denver" because of the steep vertical concrete walls that frame the sunken section of I-25 between Logan and Franklin streets.

The University Boulevard interchange is a cloverleaf no more. Now it's an SPUI - traffic-speak for single-point urban interchange. It's supposed to handle traffic more efficiently by using a single set of signals for all the cars going straight on University or turning left onto or off the interstate.

And driving through the I-225 interchange is now a breeze, untangled of the dangerous merges thanks to a flyover, a "braided" ramp and a tunnel that remove traffic conflicts and keep merging to a minimum.

Here are some of the other big changes on the 17-mile corridor:

Southbound at Broadway, you enter I-25 on a wide, smooth ramp that replaces the zigzagging entrance that was tucked like an alley behind the Gates Rubber building. Forget the old railroad track that would jar your suspension. It's gone.

Instead of being dumped immediately onto I-25 in a high-speed death merge, you've got a long acceleration lane ahead. It's called a collector/distributor, or C/D, road, and T-REX has plenty of them.

These roads, usually two lanes, are separated from mainline I-25 by concrete barriers. In this case, traffic entering at Broadway joins cars from the freeway heading for the Washington Street exit. In about a half-mile, the Washington-bound traffic goes up a ramp on the right, and the rest of the traffic merges onto I-25.

You'll find the same setup on northbound I-25 between Evans Avenue and Colorado Boulevard.

Once you're on I-25, you'll enjoy four lanes in each direction instead of three. South of the I-225 interchange, there are five through-lanes in each direction.

But that's not all.

There are additional lanes between major exits. Called auxiliary lanes, they provide up to a mile of extra driving room before motorists have to merge left into traffic or move right to get off the interstate.

The reopening of the ramps and the completion of the T-REX project is great news to nearby home and business owners.

"If I could do a cartwheel right now without falling, I would do it. We're really excited about it.. yeah," said Duffeyrole Cafe owner Nick Ault. "When CDOT and RTD were originally planning this project we thought it wouldn't be done until the summer of 2008."

The use of C/D roads and auxiliary lanes is expected to greatly improve the safety of the I-25 drive.

Before T-REX, traffic getting on northbound I-25 at Belleview had to do a dangerous merge in front of cars aiming for the upcoming double-exit lanes for I-225.

To solve that, T-REX built a braided ramp. The Belleview entrance ramp to I-25 now goes up and over a bridge. The exit lanes for I-225 are threaded under that bridge. The result is that the two conflicting flows of traffic no longer have to crisscross each other.

This braided approach is also used to separate the northbound I-25 exit for Broadway from the northbound Washington onramp.

I-25 south of Belleview has been widened to 10 lanes, but the use of full auxiliary lanes between each exit gives it extra capacity and safer merging zones.

Drivers heading up I-225 to Parker Road have three full lanes, plus a fourth auxiliary lane, between Parker and DTC Boulevard.

The T-REX corridor is peppered with high-tech tools to help traffic managers monitor conditions.

Every third of a mile, you'll see poles mounted with silver boxes pointing toward the roadway. These are radar units that automatically count vehicles - not just the total at a given point, but how many are in each lane.

Cameras every mile or so feed monitors at the Colorado Department of Transportation traffic-operations center in Lakewood. Message signs tell motorists of any trouble ahead.

In the I-225 tunnel, smoke detectors, cameras and counters watch for any stoppages or problems.

If you stay on I-25 northbound long enough, you'll go over the new Broadway bridge, with four lanes in each direction.

But after that, you're in Valley Highway territory - three lanes and a bottleneck at Santa Fe Drive.

Welcome back to I-25 stress! Highway planners have a study under way, similar to the one that led to T-REX, for this next segment up to Sixth Avenue.

But right now, there's no solution and no money on hand to build the Son of T-REX.

Some of the safety features built into the new I-25 and I-225

All signposts and other objects installed within 30 feet of the travel lanes are designed to break away to minimize damage in a crash.

Most of the center concrete median barrier has an extra level along the top called a "glare screen" to keep headlights from blinding oncoming drivers - and to prevent gawkers from slowing down to look at accidents in the opposite lanes.

Each major entrance ramp has signals to meter the flow of rush-hour traffic onto the interstates.

There are numerous gated openings along the fence separating the highway from the light-rail tracks to allow emergency access.

The entire 17 miles of T-REX is lighted from high-mast poles in the center median. Before T-REX, lights were located only at interchanges.

Variable message signs allow CDOT's highway monitors to post current road information for drivers.