1940 map of Boston Elevated Railway night service (Owl service), with color highlight of the three available modes: 
<div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:#BE2D2C;color:#202122;text-align:center;"> </div> street car (tram)</div>
<div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:#FFAB2E;color:#202122;text-align:center;"> </div> bus</div>
<div class="legend" style="direction:ltr;line-height:23px;"><div class="legend-content" style="display:inline-block;vertical-align:top;box-sizing:border-box;width:34px;height:23px;overflow:hidden;font-size:15px;border:thin solid #333;background:#2CA05A;color:#202122;text-align:center;"> </div> trackless trolley (trolleybus)</div>
Boston Elevated Railway
Map desaturated, rotated and skewed into orthogonality, staples removed; added 50% transparent overlay highlighting the three depicted modes.