98 Bridge and friends - The 98 was always the basic bridge, it had two approaches and one trestle. The No. 99 Bridge was always the same except it had two trestles or spans. When the bridge was made for One gauge track, it was numbered 98-1, when made for electric track it was numbered 98-3,  and if the bridge was for One gauge electrical track it was numbered 98-1-3. Bridges built to use with wide gauge track were numbered 99-2-3. The 99 meant 2 spans, the '-2' meant wide gauge track, the '-3' meant it had electric track, of course wide gauge bridges only came with two spans and electric track. A No. 99-3 would have two spans and be for 0 gauge mechanical track, and you thought the numbers were confusing. 

Circa 1905-1906- This was the very first bridge Ives ever produced, which even though none of them ever carried any numbers, you should know this is a No. 98. To spot this as the very first series notice the plain yellow brick litho on the approaches, the butterscotch litho on the girders and look closely the two supporting braces on the top of the bridge that keep it from folding over are strips of butterscotch lithograph. Later bridges use just a plain wire brace. Below is the same bridge except the girders are red litho and the center span has RED brick for a base.

Circa 1907-1908 - Here's a closeup of the single span from what would appear to be the same bridge, but look at the corner braces at the top of both sides of the bridge. They are just a metal stripe, making this a later bridge.

Circa 1905-1907 - Same bridge again, but this one is technically a No. 99 with two center spans. Below is the 98 with all red approaches.

Circa 1909-1910 - This is a One gauge bridge and though not as obvious it has two spans, so its number would be 99-1. The same bridge was made for three rail track and would be numbered 99-1-3.

Circa 1910-1912 - Another No. 98, Note this one has painted girders and the ramps have a sort of jungle lithograph. Below is a similar bridge looking at it from the top.

Circa 1915-1922 - No. 98 Bridge. Painted white than sprayed with green. Girders are now solid. Below is the same bridge except it has windup track - this was the color that Ives called Mottled Gray.

Another example with the mottled gray finish - this one is a No. 99 with the double center span.

Circa 1915-21 - The green example above is actually a 99-1-3 (1 gauge double bridge for electric track).  We've seen Wide gauge bridge that look exactly like this.

Circa 1923-1927 - This one is wide gauge and painted red,  number it 99-2-3. Note the simulated concrete bridge piers. Below same bridge in box.

Circa 1923-1930 -  This No. 98-3 is painted red and has a simulated concrete base. The bridge below is from the same period but would be numbered 99-3

Engineer's view of bridge.