Paris has a fine transportation system. Bus lines, the Metro, and the RER rail lines crisscross the city, significantly reducing the need for a personal car or an expensive cab.

The bus-Metro-RER troika was inadequate in one significant sense: They sent spokes out into the city, and then the suburbs, but there was no “wheel” linking them at the peripherique of the city.

That is where the Paris Tram Line 3 comes in, which we learned first-hand this week.

So, you are on the eastern side of the right bank (north side) of Paris?

Then you know it is more than a little difficult to get to the popular exposition center at Porte de Versailles, on the southern edge of the city, by using the Metro.

It is more difficult if you have any issues with long, brisk walks at changes along the route or climbing/descending stairs, which generally is inevitable, on the Metro.

Using Tram Line 3, however,a person can get from the 11th arrondissement (or the 12th, 18th, 19th, 20th) to the convention center in the south in a bit less than an hour — and never climb any steps.

From the 11th, first comes bus line 46 to the Porte Duree on the city’s southwestern edge.

Next comes the tram, a walk of no more than 50 yards.

The tram runs west along the southern rim of the city right to the Porte de Versailles, allowing a person off within 100 yards of any of the exposition centers.

The bus ride is about 20 minutes, and actually moves along more quickly than does the tram, which is above ground all the way and stops at traffic lights. The 17 stops from Duree to Versailles consumes about 30 more minutes, but no one has to climb Metro steps, remember?

That the Paris Tram fills a need is made clear by the number of people who ride the lines — tens of thousands of them daily. Our trains, going and coming, carried hundreds of people, and they could exit the tram along the way to pick up Metro lines 4, 8, 9, 12, 13, 14 as well as two RER lines.

Plans are in the works to extend the Line 3 tram another eight stops west, across the north of the city, and when that is done, Paris will be about 75 percent encircled by Line 3 — as can be seen on the map.

Which will make a handy civic transportation system even more traveler-friendly.