Just read the article on the new V&O. The addition of a lap siding was something worth mentioning but I can’t really see what the purpose of this would be? And I can’t envision how it could be configured as “one very long siding or as two shorter ones”
Any responses would be appreciated,
Shawn
I thougt it was overlapping boards on the sides of structures. LOL FRED
Ok, I created this in 10 minutes with corel photo paint, so it ain’t pretty 
http://www.sandcrawlerworkshop.com/images_old/lapsiding.jpg
Top drawing is a lap siding.
Middle drawing is a lap siding configured as 2 short sidings. A short train could be waiting on the blue siding, another on the red siding, and a third could pass BOTH of them on the black (mainline).
Bottom drawing is a lap siding configured as a long siding. A longer train could be on the blue trackage, while another train could pass it on the red trackage.
Hope this helps, and, if I’m totally off here, someone please correct me. 
Rob
That is what I was thinking. A long siding with a second entry point and second exit point. Have seen that trackage.
Saw the actual image, Overlaped sidings, the overlapped section on each side of the main. The limit length of each siding is what fits keeping the main open. But when each has the siding and part of the main, two trains, neither of which will fit either siding alone can slide past. Nice piece of track to put on a layout. What is optimum? Rather like a saw-by with two sidings used.
Perhaps the best source for answering your question is a book called Track Planning For Realistic Operation by John Armstrong. Published by Kalmbach (of course). My copy is probably over 20 years old, but this material hasn’t changed much, and I believe that it is still in print, though the cover price has certainly changed in that amount of time.
In the book figure 3-7 gives a full description of this arrangement. It basicly works as one long siding if the trains needing to pass stay to the outside. Both trains use part of the mainline and one siding, allowing two trains, both longer than either siding, to pass. It can also be used to allow 3 trains to meet, one on each small siding, and one on the main.
It doesn’t seem like that big of a deal as a stand alone concept. But when placed into the larger context that the book provides, it can prove to be a very usefull and interesting piece of trackwork.
I don’t work for Kalmbach, but I have been reading their offerings for over 30 years, and have developed quite a library of material. This book is a great reference, and I have consulted it many times over the years. Next time you are in your local hobby store look for it, and buy it. It will change the way you think about railroads!
Thanks for the information! The diagram was very helpful. And the comedy, oh the comedy… nice. I am amazed how easily people help one another in this hobby.
Shawn
The only thing I nevert understood is why install four switches and three tracks instead of two long tracks?
To save space. It also allows two short trains to be passed by one longer train, or two longer trains to pass each other–the extra track adds flexibility. A lap siding type effect can also be achieved by putting a crossover in the middle of a relatively long traditional siding, if width rather than length is an issue, as it may be on shelf layouts.
Very nice. I knew I had a problem getting one train out of yard and another in. This solved it Thank you very much!
Lap sidings are sometimes used for speed. If the railroad just put in one long siding, a short train would have to travel the whole length at restricted speed. With a lap siding, a short train can get back on the mainline faster.
Buffalo,
I am not sure about your statement, I think that every train in that siding situation needs to go slow anyway. Not to mention stopping to throw the switches. Meets between large and massive objects are very cumbersome and delicate operations in railroading.
It would take a engineer with a lack of a nervous system and large doses of Zoloft not to have some fear during high speed meets.
Frequently the siding is built to a lower standards than the mainline (at least in the old days). In this case it will have speed restrictions. Thus the train that takes the siding travels at reduced speed even though the train it met has already passed. If the siding is very long (talking miles here) this can be significant. By putting a crossover in the middle it can get back on the mainline and back up to speed quicker.
Enjoy
Paul