Two days in advance: Make cookies. Roll out dough 1/8 in. thick. Using patterns, cut 10 buildings in each size. Using cutters, cut train engine, 2 cars, airplane (trim off wings and bottom of tail; bake wings separately) and 3 trucks (cut front end off 2 trucks to make passenger cars for train). Bake and cool cookies. Prepare 2 recipes of color flow icing. Outline and flow in cookies with color flow. Let dry overnight. When dry, pipe details with full-strength color flow. Add tip 3 dot lights on vehicles and tip 1 outline spokes on train wheels. Overpipe roof of train cars with tip 3. Pipe tip 3 outline windows on buildings (pat smooth with finger dipped in cornstarch).

Ice smooth 2-layer 14 in. cake (bake two 1 1/2 in. layers to make a 3 in. high cake) and 3-layer 8 in. cake (bake one 2 in. and two 1 1/2 in. layers to make a 5 in. high cake). Prepare cakes for stacked construction. Make fondant train track. Tint 12 oz. fondant black; reserve remaining white. Roll out black fondant 1/8 in. thick; cut 1/4 in. strips for outer rail. Pipe a thin line of piping gel along edge of foil-wrapped foamcore board; attach outer rail strips. Cut and attach inner rail the same way, positioning 1 in. from outer rail. For cross rails, cut 1/4 x 1 in. black strips; attach with piping gel.

Using patterns, cut cloud and train smoke from card stock; print messages with marker. Cut lollipop sticks to 3 in. long; attach to back of train smoke cloud with full-strengthcolor flow; let dry. Attach wings to plane cookie with full-strength color flow; let dry. Attach lollipop sticks to 3 building cookies for cake top with full-strength color flow, leaving 5 in. extending to insert in cake; let dry. Attach stick and cloud to plane with full-strength color flow; let dry. Cut two lollipop sticks to 4 in. and attach to cars and truck, leaving 3 in. extended; let dry. Cut 1/4 x 1/2 in. strips of black fondant for lane dividers; position on 14 in. cake top, attach with damp brush 2 in. apart. Roll balls of white fondant; with color flow, attach to backs of train cars for additional support. Attach buildings and train cars to cake sides with dots of icing. Insert cars and truck in 14 in. cake. Insert buildings and plane on sticks in cake top.