And now, a public service message from your Port Authority:

This week, against the advice of our lawyers, mothers, riders, psychics and brothers-in-law, we have the audacity to change something in Pittsburgh.

In an attempt to minimize the rioting and mass bewilderment that may well ensue, we would like to emphasize that we're not really creating something new!

We're bringing back something you remember fondly from the past.

No, not flammable, easily derailed 1930s-era streetcars. The Overbrook rail line.

We offer this simple guide to help our customers understand the adjustments to light rail service and spend as little time as possible puzzling over which trolley not to get on or, worse, chewing us out on the phone.

Keep in mind that for the first few weeks, riders may experience some delays.

The entire line was due in 1998, for example. Thank you for your patience.

At midnight last night, the last 42L car left Downtown for Library via Beechview. If the 42S left South Hills Village at 12:29, traveling at 22 mph, at what speed must the final 42L travel in order for the trains to meet at Dormont Junction?

Extra credit: Who's asleep in the back?

On reaching the end of the line, the last 42L was decommissioned and stripped of its insignia amid solemnities including a 21-drunk salute. We encourage you to begin reminiscing about the good ol' 42L in preparation for Rick Sebak's upcoming nostalgic documentary.

From today onward, Library will be served by the new 47L Library via Overbrook line. This is the original routing along a new line with new stations that are actually more than a block apart, and no more of this dawdling through Beechview. Don't bother figuring out the new schedule. There will be another new one after Saturday.

We may change it every couple of weeks, just because it's a new line and nobody can say "I've been taking this trolley at the same time for the past 83 years!" to make us feel guilty. Passengers are advised to allow extra time. Just go to your stop and stand there until the trolley comes. There will be one eventually, and you can put your waiting time to good use by eyeing up any shady characters and their bags as potential security risks.

On Sunday, when we change the schedule you were just getting the hang of, we will appease you with free rides on the new 47L. And special inaugural celebrations at each of the new stations!

Bring the whole family for treats, memorabilia and appearances by all your favorite public-transit characters: Murray Mumbler, Cellma Yakk, Screamy the Kid, Mr. Spooky and the $#@&* Holler Crew.

There will be a snowball-bombing contest with prizes for accuracy and distance, a cross-lot park-n-ride dash and a beat-the-train competition for drivers at several grade crossings.

Commemorative coins will be flattened on the tracks.

The first 1,500 riders boarding the 47L at the new stations will be entered to win a trip for two to New York City via Amtrak, which is a lot like the T except it sometimes goes faster and has even worse financial problems.

Facts you should know:

47L passengers going to new stations from Boggs to Killarney and low-level stops must ride in the first car of two-car trains. Others can ride in the second car, but keep in mind there's no beverage-cart service back there.

Sunday is the only freebie day. We are not hauling your seersucker butt to work for nothing, mister.

And the 47L is the only route with free rides. We are not taking your half-exposed butt to South Hills Village for nothing, missy.

Oh, but we're going to change the schedule on the 42S, too, starting Sunday.

We are not, repeat not, raising the fares. It's out of the question. Nearly impossible. Unlikely. Well, we'll let you know.

Look, don't panic. You'll get used to it. Tell you what: We'll slip you a free transfer at Washington Junction if you got on the wrong line and want to continue on the other one.

It took longer than we expected, but we are pleased to reopen the new and improved Overbrook line. We suppose you'll want the Drake back now. Don't get carried away.