Disclaimer: this is mostly personal experience, and quite outdated (2015).
It depends a lot on how you define “safe” (for example, would you feel safe talking to a border guard threatening you in attempt to squeeze a bribe, but without involving physical violence?), but generally your safest route would be through Europe, Russia and China. Then you have a few choices, none of which is hassle-free:
China – Nepal (via Tibet) – India. This will require, besides a Chinese visa, a special permit for Tibet. According to a few agencies I talked to in Feb 2016, the permit required you to join an organized tour and stay with your group. Path to Lhasa would be reasonably easy (there is a train), but from Lhasa to Kathmandu you would have to hire a car – again, as part of your tour. Once you get to Nepal, from Kathmandu you can catch a direct bus to India, even all the way to New Delhi (although I’d recommend to take a bus to the border, and catch another one at the other side – it is much faster, and also cheaper).
You may hear stories about people crossing to India directly from China through Nathu La, but as far as I know, it is not opened for non-piligrim visitors.
China – [Laos – Thailand] – Myanmar (Burma) – India. Lots of paperwork. According to Myanmar authorities (Oct 2015), Myanmar-India overland border crossings were opened to foreigners. However they require special permits from both countries (i.e. to cross overland from Myanmar to India you need to get special permits – besides your visa – from Myanmar and India). This is very unreliable route. Situation in Myanmar regarding overland crossings changes often, and you’re not guaranteed to be able to continue into the country once you cross the border. For example, at Tachilek crossing you can get in (from Thailand), but cannot travel far through overland, although you can fly from Tachilek airport via domestic flight. This way you also end up in the restricted areas of India, quite far away from Delhi.
Routes via Iran and Pakistan, or through Bangladesh are also possible but less safe. Unless you have been to, and feel comfortable in strict Islamic countries – and this includes covering up yourself – I would strongly advise against this route for a solo woman. For a mixed couple or a man those would be reasonably safe though.
Above I see someone mentioning Tajikistan, but I don’t think there is a route there which does not involve Khyber pass in Afganistan (and crossing Pakistan too), and this is not considered safe for foreigners.
Now regarding the countries in your route:
Russia is relatively safe if you’re taking trains using a cheaper “platskart” class (the “coupe” class has a compartment for 4 with locked doors, and if you end up with three males who enjoy drinking, it might not be so safe).
China is safe, and this includes Tibet.
Nepal is safe. Natural dangers such as earthquake are higher risk there.
I’d say among those three you’ll have higher risk of harassment in India itself.
The UK Government has travel advisories against all travel into the area of Iran within 100KM of Pakistan. Most of the rest of that path has ony “normal” advisories.
Within Pakistan itself, the Southern route has only “normal” advisories, while the Karakoram Highway itself has advisories against all travel.
The Northern route you mention (ending through China) has no advisories against travel for UK nationals, only general precautions.
So, from the perspective of whether or not you trust your Government, the Northern route through the ‘stans would be “safer” for you.
Good luck, and safe travels.
I can answer only about Russian part of your trip.
You can avoid “Kazakhstan > Uzbekistan >Tajikistan > Kyrgyzstan”, Russia has a common border with China. It will extend you trip, but not too much.
Your best option for most of the path is train (at least for solo trip). There is a train route from Moscow to Khabarovsk which is located near the Chinese border. It is pretty safe, but you need to learn at least basic Russian because there is a chance that no one speak English.
To get to Moscow you can choose train too. Moscow is safe enough for tourists if you do not go somewhere outside tourist places at night.
If you want to have a car trip you will have rough time. Some western parts of the country can be dangerous.
Alternate Answer provided at OP’s request:
If travel from Europe to India is the goal and specifically flying is the problem, you can travel by ship.
One option is vacation style cruise lines such as Norwegian, Cunard, Royal Caribbean which sometimes offer repositioning sailings.
However, if you just want to get there, you best bet is booking on a container ship. There are a number of sites and travel agents who can help you with this such as: https://www.freightercruises.com/
The answer to your question is rather opinion based and very much depends on your personal behaviour. Meanwhile, few people who have actually traveled to Iran will call it ‘unsafe’, though of course Afghanistan and Pakistan can be quite volatile.
Plenty of people make this journey. Tony Wheeler and his wife, founders of Lonely Planet, are a well known example, who, if my memory serves me well, wrote their first guidebook on exactly this journey.
As anyone who has made this journey will tell you, it is very doable, with the most ‘risky’ section probably being south western Pakistan. More so if you need to rely on public transport. More so if, indeed, you are a woman traveling alone.
Then, there are other questions on SE that you should read; 1, 2.
Finally, if you want to avoid Pakistan altogether, you’re going to have a hard time, with your only real option being going around Tibet, and thus through China, meaning either going through central Asia or through Russia, the former adding a bureaucratic challenge, the latter adding many thousands of kilometres to your journey (even if it would be a rather awesome journey).
Credit:stackoverflow.com‘