diff --git a/simple_analysis/templates/simple_analysis/simple_analysis.html b/simple_analysis/templates/simple_analysis/simple_analysis.html
index 078b2ba..f475d40 100644
--- a/simple_analysis/templates/simple_analysis/simple_analysis.html
+++ b/simple_analysis/templates/simple_analysis/simple_analysis.html
@@ -2573,7 +2573,6 @@ let _trafficAnimId = null;
 let _trafficPlaying = false;
 let _trafficSpeed = 1;
 let _trafficCurrentTime = 0;       // current Beijing Unix time (seconds)
-let _trafficCanvasCtx = null;
 let _trafficParticles = [];        // [{src, dst, p1, p2, midX, midY, progress, speed, count}]
 let _trafficPrevFrameTs = 0;
 let _trafficAllEdges = [];         // flat array of all edges across all windows