-let first_out = Vec::<EdgeId>::load_from("first_out_file_name").expect("could not read first_out");
-let head = Vec::<NodeId>::load_from("head_file_name").expect("could not read head");
-let travel_time = Vec::<Weight>::load_from("weight_file_name").expect("could not read travel_time");
+let first_out = Vec::<EdgeId>::load_from("first_out_file_name")?;
+let head = Vec::<NodeId>::load_from("head_file_name")?;
+let travel_time = Vec::<Weight>::load_from("weight_file_name")?;