The sceniced module "Interstate" was showcased for the first time in Leonberg in February 2010. The main subject are the highway bridges which lead Interstate Highway 94 across the railroad and a small stream. Because the model railroad industry does not offer street bridges of these dimensions, they were scratchbuild from styrene sheets and profiles. The bridges have no prototype but the dimensions are typical for concrete beam bridges in North America.
The following materials were used:
0.08 in sheet for the deck
0.04 in sheet for the abutments
0.02 in sheet for the piers
0.08 x 0.08 in dimensional strip for reinforcements in piers and abutments
0.1 x 0.25 in dimensional strip for the bridge beams
0.08 x 0.2 in dimensional strip for the railing
0.02 x 0.08 in dimensional strip for the crash barriers
0.025 in round rod for the crash barriers
The bridge was painted with Tamiya colors. For masking the highway markings I used Kyosho Micron Tape 0,7 mm.
In the following text I want to show some aspects of planning and building these N scale Interstate Highway bridges.
Since I had no concrete prototype, I had to determine the dimensions of the bridges. From several sources in the internet I got general informations about the width and the thickness of the bridge deck, the matching beam cross section and the bridge field length. These dimensions were used to choose the right styrene sheets and profiles. The piers are an own design.
The module has a trapezoidal footprint. The radius of the track is 15 feet over 10°. For a pleasant look the bridges were placed off center and a little bit skewed. The clearence height should be sufficient for double stack container cars. Now it was possible to calculate the height of the bridge deck over the railheads. The result of the planning process were documented in the sketch and the CorelDraw graphics to the right.
To have an even surface for the waterbody and a solid foundation for the piers and abutments I glued two thin plywood sheets in the module skeleton. With the defined dimensions of the bridge parts and the embankment, the sides of the module could be sawed. The height of the piers and the abutments was the same as the measurement between the plywood sheet and the contour of the module side minus the bridge beam height. The street and the bridge deck is one piece of 0.08 in thick and 2.75 in wide styrene sheet. For maintenance reasons the bridges should be detachable. To avoid cleavings between the piers and the bridge beams they should be glued together.
To make the bridge piers I first cutted a jigg that I used to line mark the contours of all twelve front and back sides from 0.02 in sheet. Afterwards I glued reinforcement strips of 0.08 x 0.08 in dimensional strips in the sides as shown in the photo above. The sides are made from 0.4 x 0.02 in strips. I made the abutments twice: the first version from 0.02 in sheet was not stiff enough. The final once are made from 0.04 in thick styrene sheet. The bridge decks are easy to make, because you just have to cement the dimensinal strips for the railings on the upperside and the beams on the downside. I had already cutted the parallelogram shaped roadways to their final length before I cemented the railings and beams on them. So I had to determine the exact ends for the beams to ensure an exact alignment of the abutments. Dissenting from the drawings I reduced the clearence between the bridges a little bit (the modules contour was already sawed) to have a little bit horizontal embankment surface on the outer sides of the roadways. In the drawing and graphic the slope begins directly at the outer edge of the roadway.
In October 2009 the shell constructions of the bridges were showcased while the module was used at the FREMO meeting in Lauffen. After that event the landscaping had to begin. But where to start? After some thoughts I decided to start with bonding the abutments onto the base plate. The embankment was made from extruded polystyrene foam (XPS) while the landscape surface was made from Expanded polystyrene (EPS). Finally I covered everything with a thin layer of brown adhesive for cork tiles.
After modelling the surface I added 0.02 in thick styrene sheets on the slope under the bridges. These areas are normaly paved at real bridges.
What followed was the painting of the bridges. In a first step I roughed the roadways with very fine abrasive paper. The road markings were made "negative": I started by airbrushing a yellow stripe (Tamiya XF-3 flat yellow) on the inner sides of the roadways. I masked it with a stripe of Kyosho tape. The white stripes are unpainted styrene. To get exactly straight markings, you must not sweep along the tape with your index finger. The result will be wiggly lines. It´s better to cover the stripe with a piece of styrene and to press down along this covering. The broken traffic line was applied as a continous line and afterwards the stripes were cutted and the superfluous pieces were removed.
After some testing I decided to paint the roadways with a mixture of one part Tamiya XF-19 sky gray and two parts Tamiya XF-2 flat white.
A week later I painted the remaining areas of the bridges, the piers and the already installed abutments with a mixture of one part flat gray and four parts flat white. Furthermore I accentuated the roadways with gray artists chalk. I applied the chalk with a crumpeled piece of facial tissue.
The next step was to cement the piers to the bridges. When I tried to position the bridges I had to recognize that the holes in the EPS were not in the right locations. So I removed the EPS landscape around the piers and made sleeves from XPS which fitted exactly around the piers and were a bit smaller than the cutaways in the EPS landscape. I positioned and glued the sleeves in their exact position with the bridges used as gages. Afterwards I fitted the sleeves to the the landscape contur and filled the gaps with plaster. You can see this in the third picture at right. The last step for centering the bridges was to glue short pieces of 0.08 x 0.08 in strip styrene to the embankment for centering the roadways. For this I used white glue. The last step was to apply some more cork adhesive to camouflage the strips on the embankment.
Finally some detail pictures of the completed bridge. In the first picture you see that the roadways overhang the abutments about 0.04 inches. The outer beams are set in about 0.08 inches. The tops of the piers have the same width as the abutments.
The crash barriers are also selfmade because commercial products are ways too crude. I built my crash barriers from 0.025 round rods which I cemented flush to the edges of 0.08 x 0.02 in stripes. The studs are made from the same rod.
Cleaning the track is very easy because the bridges remain detachable and are coincidentially protected from damage.
Here a more detailed picture of the abutment. You can see the XPS core of the embankment. The slope is slightly steeper than 1: 1.5
The same picture with installed bridge showes how exactly the roadway is laying between the centering stripes. You may not suspect that the bridge is still detachable.
The width of the roadway is the only change I would make today. I made the lanes 12 and 10 scale feet wide. Two scale feet more for every lane would eventually be a bit better.
